In Washington D.C. some of the places require tickets. They're free of course but you need to wait in line early in the morning to get em before they run out. Last summer I had to stand in line T_T to go inside the Capital building, the Washington Monument also needs one to go to the top of the tower, but if standing on the ground is fine then everything's okay.
Oooh and the modern art museum is fun ^_^ my favorite exhibit was this model of a naked woman standing in front a a huge pile of clothes. Yeah I feel like that sometimes ^_~
