Park Place on the Left bank, a quarter of a mile north east of Marsh Lock.
Park Place Boathouse on the Left bank, a quarter of a mile upstream of Marsh Lock.

2016: Park Place: Britain's most expensive home sold for record £140m:

The buyer, (Russian?) who has not been identified, has snapped up the 300 year-old Grade II-listed property, in the village of Remenham, near Henley-on-Thames, Oxon. The record sale also reportedly includes about 200 acres of the parklands, listed monuments, house, cottages, stables and a boat house.
Park Place, which has 30,000 square feet of living space and is set in 570 acres, was bought for £42m in 2007 by Mike Spink, a developer who specialises in upmarket properties. At the time it was the most expensive house bought outside London.
The developer has spent several million pounds undertaking extensive renovations of the property, which had a decaying exterior and was run down. He is also developing a second 300-acre phase of the estate, which is not part of the sale.
The property, which backs on to the Thames river, was put on the market in 2006 for £45 million after plans to turn it into a luxury country club were rejected by Wokingham borough council following a vociferous campaign by residents.
The main house dates from the early 18th century and was once owned by Frederick, Prince of Wales and eldest son of George II, and was substantially rebuilt in the late 1800s. Rooms still have the original huge stone fireplaces and stained glass windows.
The ghost of Mary Blandy, who was accused of poisoning her father in 1752, is said to haunt the grounds.
The original sale involved several outlying properties, including three houses, 10 tenanted cottages and a further eight in need of renovation.
The property, which was used until 1998 as a boarding school, has two golf courses, a boathouse on the Thames and a stable block. It was recently used in the remake of the film St. Trinians.

1792: Picturesque Views on the Thames, Samuel Ireland -

Park Place, Samuel Ireland, 1792

1793:  Scene at Park Place including the Druid's Temple, Boydell -

Scene at Park Place including the Druid's Temple. June 1, 1793 J. Farington R.A. delt. J.C. Stadler sculpt. (Published) by J. & J. Boydell, Shakespeare Gally. Pall Mall & (No. 90) Cheapside (London).

1801: The Beauties of England and Wales -

PARK PLACE, THE residence of the Earl of Malmsbury, is Situated one mile south-east of Henley. The many interesting objects concentrated in this domain, are calculated to excite even the most latent energies of poetic description ; yet none of the magic tints which fancy blends to embellish the creations of imagination, are requisite to give lustre to the picture. Beauty, grandeur and variety, are the characterizing features of this estimable seat, the grounds of which display as much boldness of composition as any on the banks of the Thames. The steep sides of the hills, with their chalky precipices, are overhung with grand masses of stately beech interspersed with evergreens, which extend to the margin of the stream, and, from various points of the landscape, appear like an immense verdant amphitheatre. The projecting lawns correspond with the sublimity of the contiguous scenery, and unite in forming a diversity of rich and beautiful prospects.
This estate was purchased of the widow of the late Field Marshal Conway, by the present noble resident, in the year 1796. The General expended considerable sums in improving and embellishing the grounds ; but the principal alterations of the house have been made since it became the property of the Earl, under whose direction the arrangement and construction of the rooms have been greatly altered, and elegantly decorated from the designs of Mr. Holland, the architect.
This mansion is situated on the brow of a lofty range of hills, that accompanies the windings of the Thames for several miles ; and the spot on which it stands is nearly three hundred feet above the level of the water, being judiciously sheltered from the winds by extensive plantations. The building is composed of brick, cased with a yellowish stucco; and, though not externally grand, is highly interesting, from the taste and elegance exhibited in the interior. The library is splendidly furnished, and stored with a profusion of choice books, the chief of which were collected by the late Mr. Harris, (father to the Earl,) who was esteemed by all the literati of the day for his erudition and refined taste. This selection has been considerably increased by his son, whose additions have been principally made from the classics and historians. The taste of this nobleman for literature is displayed by almost every room in the house being filled with select volumes. This mansion contains several good paintings by ancient and modern masters. ...
Though the house, as we have already stated, is not without attractions, yet the most prominent feature of Park Place is the beautiful scenery of the grounds, which are diversified with a continued succession of lofty eminences and low vallies. The woods partake of forest wildness, and being intermixed with shrubberies, produce the most picturesque and beautiful views. Many of these scenes would delight the mind of a Salvator, and many others a Claude might in vain attempt to copy. Some of them command an unbounded horizon, and present all the variety of English landscape.

On the east of the mansion is a garden inclosed and laid out according to the French taste; and near this is the aviary, designed on a peculiar plan, and furnished with a beautiful selection of the feathered race; among which the silver pencilled and gold Pheasants are particularly deserving of admiration, for their pleasing forms and elegant plumage.
A winding subterraneous passage, nearly 170 yards in length commencing in a wood on the summit of a hill near the aviary, leads to a fine valley, planted on the borders with cypress and other trees. Here a grand colonnade, representing a Roman amphitheatre falling into decay, and majestic even in ruin, presents itself. This is executed in a manner far superior to most ornaments of this kind; and its secluded situation, and mouldering ivy-crowned walls, render it peculiarly picturesque.
Descending the valley towards the Thames the path winds under a large arch, curiously constructed with natural stones, of vast dimensions intermingled with the enormous blocks of massive wall brought from Reading Abbey. This fabric, interesting for its singularity, seems a very romantic object, when viewed from the water on the opposite bank of the river. The High road which passes over the arch, is excluded from sight by shrubberies and plantations; and through that judicious management is prevented fom having a displeasing effect.
On a hill, near this structure, is an elegant cottage, whence the views are particularly fine. On the west the Thames glides in full stream, washing the skirts of the wood toi the whole extent of the grounds. Towards the east the meanderings of the river are indistinctly seen through the verdant scenery that adorns the eminence on which the cottage is situated. On the north the Church of Henley, and the woody hills of Oxfordshire in the distance, constitute an agreeable prospect. From the river banks in this quarter, a narrow pass, overhung with trees, leads to a chalk cavern of large dimensions. Proceeding southwards, a solitary willow walk, on the borders of the stream, conducts the wanderer's feet to an elegant tomb of white marble, composed in the Roman style and perfectly in unison with the sequestered and lonely spot on which it stands. At some distance is a romantic arch, constructed with rude stones, and rendered pleasing by the variety of its verdant accompaniments.
The high grounds on the north towards Henley are crossed by a noble terrace of great length, whence a complete birds'-eye view of the river, the town and the surrounding country, enchants the sight of the spectator. Beyond the terrace is a pleasant valley, consisting of about twenty acres, called the Lavendar Farm, exclusively appropriated to the cultivation of that herb, and separated by a line of shrubs from a steep and rugged ravine, where the high road formerly ran; the sides of which exhibit a variety of rude and broken scenery.
Near the bottom is a small stone house, much admired for its elegant simplicity. These different objects form a landscape of very distinct character from any of the prospects before described.
On a well-chosen eminence, near the southern quarter of ths ornamented grounds, stands a curious vestige of the manners of antiquity. This is denominated a DRUID'S TEMPLE, and was presented to General Conway by the inhabitants of the isle of Jersey, as a testimony of the respect and gratitude due to his vigilance as a governor, and to his amiable qualities as a man. This invaluable gift was accompanied by an appropriate and forcible inscription, which we shall transcribe in the words of the original.

Cet ancien Temple des Druides
decouvert le 12me. Aout, 1785,
sur le Montagne de St. Helier
dans l'Isle de Jersey ;
a été présenté par les Habitans
a son Excellence le General Conway,
leur Gouverneur.
Pour des siecles cache, aux regards des mortels,
Cet ancien monument, ces pierres, ces autels,
Ou le sang des humains offert en sacrifice,
Ruissela, pour des Dieux, qu'enfantoit le caprice.
Ce monument, sans prix par son antiquité,
Temoignera pour nous à la postéritée,
Que dans tous les dangers Cesaréee* eut un père,
Attentif, et vaillant, genereux, et prospere:
Et redira, Conway, aux siécles àvenir,
Qu'en vertu du respect dû à ce souvenir,
Elle te fit ce don, acquis àa ta vaillance,
Comme un juste tribut de sa reconnoissance.

The stones which compose this temple are forty-five in number, and were all so carefully marked when taken down, as to be re-erected on this spot in their original circular form. They were discovered in the summer of the year 1785, on the summit of a rocky hill, near the town of St. Helier, by some workmen who were employed to level the ground as a place of exercise for the militia, and before that time were entirely hidden with earth, which appeared raised in a heap, like a large barrow or tumulus. The circumference of the circle is sixty-six feet ; the highest of the stones about nine. They are from four to six feet in breadth, and from one to three in thickness. The entrance or passage faces the east, and measures fifteen feet in lenglh, five in breadth, and four in height. The inside contains five cells, or cavities, varying in depth from two feet four inches to four feet three inches. The coverings of these cells and of the entrance are of stones from eighteen inches to two feet thick.
Within this temple two medals were found : one of the Emperor Claudius ; the other so obliterated as to be unintelligible. The accounts of the history and antiquities of Jersey are very imperfect, yet it seems probable, that it was once particularly the seat of Druid worship. So lately as the year 1691, when Mr. Poindextre wrote some tracts concerning it, there were no less than fifty assemblages of rude stones, which that gentleman considered as Druid temples or altars; yet nearly the whole of these antique memorials have since been demolished. When, or by whom, the present structure was covered up is unknown ; but it is supposed to have been buried by the Druids themselves, to preserve it from the violence and profanation of the Romans. All the stones with which it is formed are as rough and unhewn as when taken from the quarry. This curious structure seems to be a combination of the Cromlech, the Kistvaen, the stones of Memorial, and the pure druidical, or bardic Circle. It is a very singular relict of British antiquity, and highly deserving of preservation as a vestige of the customs of remote ages.
Park Place includes an area of 400 acres; an extent of ground, perhaps, that comprises as great a variety of interesting prospects, as any of similar limits in the kingdom.

1811:

Park Place, 1811

1817:  The Druid's Altar at Park Place, Henley/Seat of the Earl of Malmesbury, Cooke's Views of the Thames

Druid's Altar at Park Place, Henley
Seat of the Earl of Malmesbury. Drawn by the late Wm Alexander F.S.A. of the British Museum. Engraved by George Cooke. Jan 1, 1817.

1821:  Park Place near Henley, Seat of the Earl of Malmesbury, Cooke's Views of the Thames -

Park Place near Henley
Seat of the Earl of Malmesbury. Drawn by P. Dewint. Novr 1, 1821.

1830: Tombleson -

Park Place Henley,Tombleson 1830

1859: The Thames, Mr & Mrs Hall

THE BOAT-HOUSE AT PARK-PLACE

We now approach one of the cultivated "lions" of the Thames — "Park Place", famous in the annals of the river for the beauty of its site, the growth of its trees, and some circumstances which give it interest beyond that of ordinary demesnes. The house was built by the Duke of Hamilton: it was some time the residence of Frederick, Prince of Wales, the father of George III.; but it is mainly indebted for its many attractions to Marshal Conway, who, towards the close of the last century [ the 18th century ], became its possessor, and who "set himself the task" of giving to Nature all the advantages she could derive from Art. The grounds have since received the benefit of time; they have not been neglected by successive lords; and the gentleman who at present owns them has evidently studied, by all the means at his command, to render them — what they are — "beautiful exceedingly". Visitors, by whom access on fixed days is easily obtained, land at the very charming "Boat-house" we have pictured; it is, in reality, a furnished dwelling, and contains some fine, and several remarkable, works of Art, — statues, pictures, wood-carvings, and foreign curiosities, — in the examination of which half an hour may be profitably expended.

A walk through the grounds, however, is a more exquisite treat — hill and dale, richly-wooded slopes, and shaven lawns, are happily intermixed; while every now and then judicious openings supply views of the Thames underneath, or the landscape far beyond. Here and there, on green hillocks or in gloomy dells, mimic ruins have been introduced; some of them built out of the debris of Reading Abbey. In one of them is a long subterraneous passage (cut through a chalk bed), leading to a Roman amphitheatre, the base of which is planted with the mournful cypress. This is the work of Marshal Conway;

THE DRUID TEMPLE AT PARK PLACE

but there is an object of greater interest in these grounds, although its value is lessened by the knowledge that this also is "artificial". Strictly speaking, however, artificial it is not; for the Druidic Temple which stands on the summit of one of the small hills, was placed exactly as it was found, keeping precisely the same form and character it received from the hands of the "builders", it may be twenty centuries ago. We may briefly tell its history. The temple was discovered on the summit of a high hill near the town of St. Helier, in the Isle of Jersey, on the 12th of August, 1785; it was entirely covered with earth, having the appearance of a large tumulus, and was laid bare by workmen employed to level the ground. Fortunately, General Conway was then Governor of Jersey; his attention was at once directed to its preservation; and, on his leaving the island, it was presented to him, and by him removed to Park Place.
"This curious structure is sixty-five feet in circumference, composed of forty-five large stones (measuring, in general, about seven feet in height, from four to six in breadth, one to three in thickness), and contains six perfect lodges, or cells. The supposed entrance, or passage, faces the east, and measures fifteen feet in length, and four feet and upwards in breadth, and about four feet in height, with a covering of rude stones from eighteen inches to two feet thick. In the removal of this curious temple from Jersey, all the parts were marked with such care as to be correctly placed in their original form, and precise direction, when they were re-erected on the charming spot which is distinguished by them. In the eighth volume of the 'Archaeologia', a particular account is given of this venerable antiquity." *
* We have retained the popular term "temple", as applied to this antiquity; but it is properly a tomb. Recent researches in Jersey and Guernsey have sufficiently established that fact. The circle of stones formed the wall of a small chamber, which was covered by heavy slabs; the "cells" contained bodies of the dead. A narrow covered passage led to this chamber, and a mound of earth was placed over all. In the thirty-fifth volume of the "Archaeologia", Mr. Lukis, of Guernsey, has described several of these burial-places, from his own investigations in these islands. He describes the avenue or entrance to them as rarely more than 3 feet in height by 2 feet in width; the interior chamber of the largest was 8 feet in height, 45 feet in length, and 15 feet in width; the roof stones, of granite, were computed to weigh thirty tons. They appear to have been used for successive interments of the aboriginal chieftains of the islands, and have been found with additional chambers as the original ones became filled with the "great departed". Sometimes in these chambers skeletons are found; sometimes bones, which show that the body was consumed by fire; sometimes the ashes are preserved in urns, rudely decorated with incised ornament. The other articles found in these tombs tell of an early and primitive people, such as spear and arrow-heads of flint, as well as knives of the same material, rudely formed beads of coloured earth, bracelets of jet,&c.
We ask the reader to pause awhile at this pleasant "Place", and give a few moments' consideration to another subject which may be suggested to his thoughts in various parts of the river; and nowhere, perhaps, will it occur to him more forcibly than it doe here.

1870: (from From Berkshire by Nikolaus Pevesner, 1966) -

The present house is by Thomas Cundy, 1870, in a rather dreary French Renaissance Style with a tower over one corner of the facade and Pavillion roofs. This house takes the place of that of the Conway family.

1881: George Leslie, "Our River" -

Once above Marsh Lock the whole character of the river is changed, a steep hill and cliffs is on the left hand, open meadows and poplars on the right, and a great, calm, wide reach of deep water and sluggish stream, partaking of the character of a small lake;  the punting is very bad;  the tow-path side is fringed all along with soft green sedges and persicaria, the sure indicators of mud.  The wooded side, though the bottom is hard, is very deep, and the projecting willows make it rather awkward, so if the wind is fair, I should have no hesitation in setting sail. 
The grounds of Park Place come down to the river's edge, just above the Mill garden, passing underneath the roadway by a picturesque arch, through which a glimpse of what is known as Happy Valley is obtained.
The Wargrave Road, which runs through the woods and over the arch, is the one traversed by Mr. Black's phaeton on its tour, and a prettier, shadier drive does not exist anywhere.  The grounds of Park Place have been divided into two parts since Walpole's time, and on the second half a house called Templecombe has been erected.  In the grounds of Park Place is a Druid's Temple, the stones of which were brought from Jersey and presented to General Conway.

[ I know its valuable heritage and all that - but, is it the planners or the County Council or the landowner to blame for the retention of the happy valley narrow bridge here which causes such danger and delay to motorists on the Henley Wargrave Road?  It should not be too difficult to rebuild that bridge at double width to solve that problem?  (The underneath of the bridge can just be seen in the Frith photo of the boathouse below)]

However, I have just come across this in Samuel Ireland's Picturesque Views on the Thames, 1799:

A great part of the remains of this venerable abbey [Reading Abbey], were removed a few years since by General Conway, for the purpose of building a bridge contiguous to Park-place, on the road between Henley and Wargrave.

And this from Rambles by Rivers, James Thorne in 1847

The huge masses of wall that remained [of Reading Abbey] were regarded as a quarry. ...
the last appropriation of them on a large scale was by the late General Conway, who, having a taste for antiquities, built a fantastic modern-antique bridge across the Wargrave-road, to connect the two sides of his estate;

[So it is, sort of, a second hand ancient monument? General Conway specialised in second hand monuments!]

1881: George Leslie, "Our River" -

The well-known boat-house with its little saint, though rather artificial, is very pretty, and the whole bit would be quite charming if it were not for an ugly trespassers' board.

[ I love George Leslie's ability with language. Makes you wonder what might happen to more attractive trespassers!]

UGLY TRESPASSERS WILL BE PROSECUTED ...
( Pretty trespassers may be invited up to see my boat house ... )

1893: Boathouse above Marsh Lock, Francis Frith -

1893: Boathouse above Marsh Lock, Francis Frith

1881: George Leslie, "Our River" -

There are several reaches of the river in which chalk cliffs rise on the banks, as those at Park Place do;  at Harleyford, Quarry Woods, Hartswood, Pangbourne, Shiplake, and in parts of Cliveden.  The chalk cliffs give great variety to the beauty of the scenery, but at none of these spots is their arrangement so perfect as at Park place;  here there is a sort of undercliff between the base of the chalk and the river, which is covered with delicious foliage, a number of most graceful ash trees supplying the greatest amount of the beauty.  These trees are rather delicate in our climate;  they likewise require a good supply of moisture, and here in the snug shelter of the chalk cliffs, with the rich soil beneath them, and the water never failing their roots, they grow in their utmost luxuriance.  From the Wargrave Road above the cliff I love to look over and down on to the tops of these trees, and realise the beautiful way that foliage must appear to birds.  The ash was Constable's favourite tree;  the exquisite grace of its branches, the sad poetic tone of its foliage, and the pale olive grey of its bark, rendering it very dear to him.

1884: The Upper Thames, Harpers New Monthly Magazine -

... like a calm inland lake, bordered on one side with woodland heights, and on the other by miles of verdant meadows.
We pause to take note of a grand cluster of beeches that are repeated in the silent river below, repeated with the last rays of the setting sun gilding their autumn-tinted branches, while the leafy heights of the grounds of Park Place make a long line of gold and green and red as far as the eye can see. Above us a clear sky, with great sun-bronzed clouds sailing away eastward, and a long line inn of crows making for some distant rookery.
Suddenly, close inshore, a shoal of tiny fish are leaping in and out of the water, like, on a small scale, flying-fish at sea. They might be suspected of a joyful demonstration in thus challenging the golden beams of the sun, but they are, in their little way, engaged in a tragedy rather than a comedy. It is a Thames pike hunting his evening meal that excites these tiny inhabitants of the river to this somewhat unusual demonstration.

1949: Park Place -

Park Place in 1949