The Mansion on O St, near Dupont Circle in Washington DC, was founded by H.H. Leonards-Spero and opened on Valentine’s Day, February 14, 1980. The house itself boasts "over 100 rooms and 32 secret doors" spread throughout four maze-like floors. Part of this elaborate layout is due to the strange design of the mansion, which is not a mansion at all, but actually four row houses opened to one another and turned into one elaborate hotel/museum.

Though a few items are part of the O Mansions "permanent collection," for the most part every item of which there are many thousands piled throughout the mansion -- many of which are acquired from local junk shops and garages sales -- in each themed room is for sale, including the thousands of books on the numerous floor to ceiling bookcases.

Because the Mansion also functions as a hotel not all rooms will necessarily be open to the public at the time of your visit, even so, a self-guided tour of the house can still take hours. Each themed room -- some themes include a log cabin room, the french renaissance room, and the billiards room -- contains hundreds of pieces of art, books, and other "treasures" to examine and ponder. The mansion also includes also a large amount of Beatles and John Lennon memorabilia, including a Sgt. Peppers jukebox in the "Beatles Room." Perhaps the best room in the hotel is the penthouse which has a somewhat seventies theme and features a large wooden hot tub.

The O Mansion is also features concerts, brunches, lunches, dinners and events, though their most popular events are their Teas, all of which must be booked online. The O Mansion is open to the public on Sunday, Monday, and holidays.