Many friends and I have enjoyed visiting the International Spy Museum (Gallery Place/Chinatown Metro Station). Admission is $13 and it should take from two to three hours to walk through all the exhibits.

If you enjoy performing arts, I suggest that you try to attend a performance at the Kennedy Ctr for the Performing Arts (free shuttle from Foggy Bottom/GWU Metro Station every 15min). The Washington Opera, Lyon Opera Ballet and Nat'l Symphony Orchestra have performances from Maundy Thursday through Holy Saturday.

I also hear that dining on board a ship on the Potomac is very pleasant.

If you tell me more about your interests, I'll try to give more specific suggestions.

Best,
bkong