Edinburgh's "Our Dynamic Earth" visitor attraction is free this weekend (Sat/Sun) in a special event to celebrate Homecoming 2009 and its own 10th anniversary.
The attraction itself is a sort of science centre, that deals with the history of out planet and the facts surrounding it. If you haven't been before, my description isn't really doing it justice; it is well worth a visit. Normally costs a fortune for a small family!
Note all scheduled tours will be on a first come first served basis.