The Old Kingdom, Old World of Darkness
Magical location. Lots of Charter magic stuff. See the Wikia page for more.
Running water. (That definitely has some sort of mechanical effect on Free Magic and Dead creatures.)
The room under the waterfall.
The sendings. (Should sendings be a Background, maybe?)
The library. (And how!)
Various specialized rooms (e.g. isn’t there an Observatory up top?) that could potentially help with checks/rolls, etc.
Mogget. (Who might be a familiar of sorts, but really, he seems to go with the house. Well, the role, really.)
Exact location of house is unknown to the general public (S.52).