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A unique hybrid of a small private luxury hotel and a museum. Contains hundreds of rooms, a collection of 20,000 books, dozens of secret passages, a collection of John Lennon's guitars, modern art and curiosities of all stripes in every room (virtually anything of which is for sale if you're interested), frequent concerts by legends of rock and R&B, numerology evaluations, banquets, etc., your curiosity will probably find enough piquing here to justify the advance reservations for tours. It's also a luxury B&B, if you are looking for extremely eccentric accommodations in the city.
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Competing with the Smithsonian for top castle status in the District is the Victorian mansion of Christian Heurich, who immigrated to the states from Germany to become a wildly successful real estate baron and brewer. He also holds the title of world's oldest brewer, having kept up his work until his death at a ripe age of 102. It's a striking example of Victorian architecture and design, and even if you don't make it to a tour, there's a nice Victorian garden in the back open to the public M-F 10AM-4PM, spring-fall.
Society of the Cincinnati headquarters and museum
The 55,764-square-foot Anderson House, which is perhaps better described as a castle, was built in 1902-1905, as the home of Larz Anderson and his wife. Upon Anderson's death, the house was given as a gift to the Society of the Cincinnati which was something of an American noble order dedicated to preserving the legacy of the American Revolution founded in 1783 after the Revolutionary War. The house serves as the organization's headquarters, and houses a museum and library with information relating to the Revolutionary War.
The Phillips Collection, opened in 1921, is America’s first museum of modern art. Featuring a renowned permanent collection of nearly 2,500 works by American and European impressionist and modern artists, the Phillips is internationally recognized for its incomparable art and for its intimate atmosphere. Housed in founder Duncan Phillips' 1897 Georgian Revival home, The Phillips Collection is widely regarded as one of the world’s finest small museums.
Cosmos Club
Almost completed rebuilt by heiress Mary Scott Townsend in 1899, the house features a Beaux Arts, Louis XVI French-inspired design. Townsend lived there until she died in 1931. For a period of time before World War II, Sumner Welles, the son-in-law of Mary Scott Townsend and Franklin D. Roosevelt's Under Secretary of State, lived in the Townsend Mansion. The Cosmos Club, a private social club, bought the house in 1950, and continues to occupy the mansion.