The sprawling estates, all built before 1950, now serve as research labs, country clubs, museums and educational centers — whether through endowment or outright purchase. Some remain in private hands while others are now publicly owned.
The Biltmore Estate was built between 1889 and 1895 for art collector and rich scion George Washington Vanderbilt II. Open daily for self-guided tours, the most massive of the outsized Vanderbilt homes covers nearly 179,000 square feet.Oheka Castle, Huntington, New York
Funded by financier Otto Kahn between 1914 and 1919, Oheka Castle is now a privately-owned luxury hotel and event venue. Kahn built the 109,000-square-foot house after selling his country estate in Morristown due to antisemitism in that community.The Arden House on railroad tycoon Edward Harriman's estate covers more than 97,000 square feet. Now a conference center with 97 guest rooms, the house took five years to complete.