My submission to start this off is the Van Slyke Castle, located within Ramapo State Park in NJ. I planted a geocache there and realized the subject would make a good locationless cache that won't be an easy log. The info below is taken directly from the park website.
THE VAN SLYKE CASTLE
Ramapo Lake was formed 12,000 years ago during a glacial
retreat. When Dutch settlers found it, They named it
after the muskrats that lived there -- Rotten Poel (Rats Pond) but the
English only heard Rotten Pond and the name stuck. In the later part
of the 19th century, Jacob Rogers, the son of the founder of the locomotive
industry in Paterson, N. J., assembled a three square mile tract of land
around the Pond from a dozen parcels of land. He greatly increased the size
of the Pond by placing a stone dam across its outlet. Rogers died in 1901,
and his will directed that the property be given to the Metropolitan Museum
of Art. That organization leased and sold it to Howard P. Frothingham, a New
York financier and avid fisherman in 1905. It was thought that he
would turn it into a first rate game preserve.
After changing the name of the lake to "Le Grande Lake", however, he sold
two years later to Pliny Fisk, an associate. Fisk was expected to establish
a community similar to Toxedo Park on the property. The realization of this
scheme, however had to wait the purchase of the property a year and a half
later by William Porter. He divided the land between two corporations: The
Ramapo Club and Ramapo Park. The former owned the lake and a strip of land
around it, and the later, the hilly woodland. This procedure would allow
owners of houses on the hills to share the use of the lake. Porter built
himself a house (which later came to be known as Van Sly Castle), but his
death only a few years later led to the abandonment of the plan. The Club
was merged into the park in 1914, and the subsequent history of the
corporation is unclear.
Clifford F. MacEnvoy appears to have gained
control of it in the early 1920's. He was a wealthy developer, and was a
general contractor for the construction of the
Wanaque
Reservoir. He built a house on the large mountain northeast of the lake.
The state purchased what is now the Ramapo
Mountain forest from his estate in 1976.
The history of Van Slyke Castle revolves largely
around Ruth A. Coles and her husbands. Coles was a nurse who had the good
fortune to care for Charles E. Halliwell, a captain of industry in New York.
She became his second wife in the fall of 1906. He died a year later leaving
her one and a half million dollars, a large fortune in those days. in 1909,
she married William Porter, a stockbroker and close friend of her former
husband. At that time, Porter was building a house on Fox Mountain above Le
Grande Lake, which he called "Foxcroft". Porter died in an automobile
accident two years later before he could realize his development of the
former Rogers' tract. In 1913, Cole married her third husband, Warren C Van
Slyke, an attorney. He was an assistant to the chief of naval intelligence
in World War 1, and later argued the claims resulting from the sinking of
the Lusitania. They lived near Jamaica, Long Island. After Mr. Van Slyke's
death in 1925, his widow lived year around at Foxcroft. She died in 1940 at
the age of 63. Foxcroft was left to her family who promptly sold it. In the
early 1950's it became involved in a bitter divorce and was not used.
Vandals soon broke in and finally torched the mansion in 1959.