Witley Park is a real place, and Whitaker Wright was a real person: the facts of his life and home are deeply bizarre and worth reading about, but they'd also be worth gaming about, so here they are recast for fantasy and rewritten for gaming (with some of the facts chopped around and telescoped together, but still. Spoilers at those links for, uh, the rest of this post). This is the kind of mysterious location with legends attached you could put near any small town, or a little way outside a city, and drop hints about. It works best as a scandal from the generation before: everyone remembers it, or remembers someone who does, but now they’ll only whisper it, and nobody knows the truth of it.
In my father's time, a man appeared in the city – first at the house of the assayers, then at the miner's guild, and then, not long after, at court. He gave a meaningless name, Whitetaker, transparently false, and he had no pedigree, and was of no account – and yet, he was in the presence of the king, weeks after he had first come through the city gates. He carried with him a bar of silver-white metal – he said it was metal - with a strange sheen, like cloudy ice, and though it was as long and thick as a man's forearm, it was lighter than lamb's wool. He had the ingot assayed, and though it seemed impossible, the alchemists there said that it was a kind of silver, harder than forged iron but workable. He spoke of a mine, far from the city, wherein he had found it, and where he would be pleased to make more of it available to his majesty.
Before long he was a favourite of the court, and of the king especially: a charmer, a man who knew he was suspected of being a rogue and played the part with joy, but who worked assiduously on those who doubted him or looked down on his namelessness. Above all, he charmed the friendless king himself, and promised him that the mines would be at his highnesses disposal. In private, he whispered too of other powers the stones had. All that he needed, of course, was a little money, and a foothold in his majesty's society: a bride, perhaps, an eligible bride like the Witley heiress – the closeness of their names was pleasing, was it not, your majesty, fitting, a sign even, perhaps, just as my coming here was a sign that your age shall be a great one?
As soon as he became the tenant of Witley Park, he upheaved the ancient building and its grounds, levelling hills here and raising them there, scattering follies and throwing up new wings onto the cowering shell of the old house. He carved out a great bowl of earth where the dancing lawn had been and diverted a stream, creating a deep lake in the centre of the park. The balls and hunting parties were legendary, and the king was frequently in attendance.
But in time, the questions that had long been asked by the old guard and by the more level-headed alchemists became too loud to ignore. The questions of the mine's location, of its prospects, even of why there could be no map of the place, were asked more and more loudly. The king submitted to his counsellors, ceased to appear at Witley Park, and many followed suit. Two years after his arrival, his name was already being forgotten when the mansion, still unfinished, burned to the ground. Whitetaker, his wife, and dozens of servants vanished in the blaze, as did the silver. The estate passed to a distant branch who never deigned to visit the pile of ash, and the brief society fame and notoriety of Whitetaker was forgotten.
Witley Park is about 10 square miles of landscaped park, with a high (6') but mostly unmaintained stone wall running around the outside. The track from the nearest settlement, largely overgrown, ends in a gatehouse and iron gates – once painted a pearly silver colour, now mostly peeled off – but there is nobody to man it. Careful checks will nevertheless reveal that by crossing the wall or the gate, the party triggers a magical alarm somewhere. The grounds are mostly trackless and heavily obscured with undergrowth, and surprisingly rich in wolves, d6 of which will attack the party at some point. Careful searching might reveal a butchered sheep left out for them intentionally under a large ash tree. There are also, scattered around, a handful of statues and architectural ornaments: a small colonnade, a faked-up ruin of a temple, a large stone table, a stone pyramid the height of a man (this last one is on the far side of the grounds from the gatehouse).
In the rough centre of the grounds is the wreck of the house, on a rising ridge of ground: if approached from the gatehouse, there are the remains of a large circular driveway in front of it. Behind it, where the ridge slopes down again artificially sharply, is the lake. The house itself is a large mass of ruins: beneath the layer of topsoil and creeping plants that has grown over it, there are still several feet of compacted, fine ash, which might be recognisable to a knowledgeable PC as the characteristic ash of magical fire. The floorplan is still clear: two wings curling around the driveway from the main section, and projecting behind, looking over the lake, a third one, which has a great deal of ironwork and shards of glass. Poking around at night will attract the attention of d6 shadows, the unhappy remnants of the servants burned to cinders in the blaze. A diligent search will also turn up, sheltered by a corner of masonry in one wing, several fine pieces of jewellery worth maybe 500gtogether (somewhat fire-blackened but cleanable) and elsewhere a few pieces of cutlery and so on.
The lake is elliptical and about 400ft long on the long side: in the centre of it, 200ft from each of the
Should this happen, or should anyone dive into the lake intentionally, they may discover somethingquite interesting. Around the sides the lake is nearly 50ft deep, but in the middle something rises out of it: a glass dome, sitting on the bottom of the lake. This is the great secret of Witley Park. The dome is about 50ft wide and rises in a perfect hemisphere: at its top, a stone shaft ascends to – or descends from – the statue in the centre of the lake. Between the two rocky outcrops there is a heavy wooden door, with a rusted lock that could be picked or forced with difficulty. Attempting to do this will, however, awaken the statue, which is a gargoyle and will attempt to throw the PCs off the small artificial island (about 10ft wide, so it's a tight squeeze in the first place) and to hold them under the surface with its trident.
If the door is opened, it reveals a narrow ironwork staircase spiralling directly down into darkness. It hits the top of the dome, where there is a hatch that opens onto further ironwork stairs, hugging the inside of the dome and descending to the flagstone floor of the dome. The dome itself is extraordinary: hundreds of panes of glass through which faint, shifting green light filters. On one side, a tunnel disappears into darkness. Most of the floorspace beneath the dome is taken up with an elaborately equipped alchemical lab, most of which is quite clean and still functioning.
Whitetaker is still down here: after a fashion, he is still alive. If your party can deal with a lich, have him be a lich: otherwise he is a wight but with a certain amount of spellcasting (something like - bane, cure wounds, inflict wounds, hold person, silence, bestow curse - or whatever will offer the party a challenge. He's understandably reluctant to use powerful magical projectiles in his current spot). He has been down there for nearly half a century now, living an increasingly horrible half-life thanks to the metal, which he stumbled upon as a young man in some far-off place. It is not quite the philosopher's stone, but he sincerely believes and has done for fifty years, that he is within a few days' work of replicating and perfecting it. He sneaks out occasionally for further supplies: the tunnel that leads off from the dome comes out under the pyramid in the grounds, which has an artfully concealed exit. This he does only at night, believing that unfiltered sunlight is fatal to him and destructive to his experiments and that only in this chamber, shielded from physical and magical scrying and from atmospheric effects and interference by the weight of the water, can his work be carried out.
He is wrong about most of this and wrong that he can get any closer to immortality than he already has: and he is gradually using up his materials and has no way of replacing them. Nevertheless, the stone, now worn down to a pebble-sized nugget, does give a kind of suspension of life – including of most of its positive effects – if used as a reagent in the creation of a draught only he now comprehends. Perhaps the information can be beaten out of him or gleaned from his notes: perhaps the useless stone can just be sold for enormous sums.
He is insane, of course, and will try and kill the party: since they are up on a precarious stairway when they first enter, he will have a handy head start. Above all, he fears the theft of his research, and if he thinks the fight is not going his way, he knows which reagents on his benches will create an explosion powerful enough to cave in the glass and bring the lake in on everything. He will not hesitate to do it.