This was the only slightly less grand mansion down the road from Marble House to which Alva Vanderbilt repaired after her second marriage. While the Vanderbilts were avid yachtsmen, her new husband, Oliver Hazard Perry Belmont, was a fanatical horseman. His 60-room house contained extensive stables on the ground floor where his beloved steeds slept under monogrammed blankets. (The Belmonts were instrumental in building New York's famed Belmont Racetrack.)

The castle, intended to resemble a European hunting lodge, has a ponderously masculine character, understandable in that it was designed for the bachelor Belmont before he won over vivacious Alva. It contains artifacts from the medieval era through the 19th century, including stained glass, Japanese cabinetry, a full-size replica of a gaudy Portuguese coronation carriage, and French Renaissance furniture. Thomas Edison designed the lighting. There are 14 secret doors and a tunnel to the kitchens, which were located 2 blocks away for fear of fire. The castle sold for a mere $25,000 in the early 1940s to the family of Harold B. Tinney, members of which still live here.

There are evening ghost and candlelight tours (with champagne) on some nights; tickets are $30 and reservations are wise.