We crashed at the Generator Hostel for a couple hours before going to the British Museum, open till 8:30pm on Thursdays, or so the guidebook said. Turns out to be no longer true.
We needed a long walk and a destination open late at night and found the perfect solution--the London Eye. Big Ben obligingly chimed 7 o'clock for us as we crossed the Jubilee Bridge.
Elgin Marbles, British Museum
Jet lagged at the British Museum--couldn't quite make it to the Lewis Chessmen.
Dolbadarn Castle, Wales
Our first castle--kids found a secret passage and climbed through. Graffiti carved into slate from 1888.