One of the last remaining symbols of true American grandeur in the Thousand Islands, this sprawling stone mansion built by Waldorf-Astoria Hotel owner George C. Boldt casts a regal presence over Heart Island and the shoreline of Alexandria Bay. With turrets and tunnels, a drawbridge, a Gaudí-like kid's playhouse, its own power house, and formal gardens, the castle and all its pieces are dazzling -- and look entirely out of place today. The home comes with a sad tale: Boldt had the castle built over the course of 4 years to give to his wife on her birthday in 1904 -- Valentine's Day -- but she died a month before and the castle, 80% complete, was never occupied. After falling into disrepair, it's been slowly restored, but by design will never be more than 80% complete. The few restored areas are gorgeous: There's an oval stained-glass window in the foyer ceiling, a formal dining room, an impressive billiards room, and the most recent renovation: George Boldt's bedroom. (Coming soon: renovations of the rooms intended for Boldt's wife and daughter.) But most of the house is still gutted, so you won't spend as much time as expected during your self-guided tour. Still, bring a picnic lunch and enjoy the 5-acre island's grounds. Then take the shuttle to the Yacht House and check out Boldt's amazing collection of antique wooden boats.