This was once the estate Herald Irving Pratt, the son of an oil magnate. The Georgian style mansion is now used as an active holocaust museum. Several other structures that are abandoned are still to be found. Such as the boiler house, a log cabin, a greenhouse and caretakers building. Many of the trees on the landscape were planted by none other than the Olmstead family that created Central Park. There is an old usenet article from 1994 that claims that the author found a secret government lab in the tunnels under the estate. Efforts to contact the poster were in vain. Click here to see the part of the estate that is now the
Webb Institute.

Excerpt from the original usenet posting from Chris Cebelenski:
From a (mostly) covered hatch in the Wellwyn (sp?) preserve you can enter
the oldest of the tunnels, which consist of a long lost government research
center and LOTS of neat abandoned rooms. We've dubbed this "The Lost City",
and it is REALLY extensive. From things I've found there I'd probably date
it to the 1950's. All sorts of abandoned labs, sealed rooms, deep shafts,
etc.