What to do on a rainy day?

What do you like to do when it rains all day?  We went out for breakfast and then went to see 'Diary of a Wimpy 2' (funny).  That killed about 4 hours in the day...what to do with the other hours.  Lego, video games, tv...nothing very active.  Do you have any suggestions that involve getting active while inside the house?  I am scratching my head and the only thing I can think of is Nerf Tag.  That only works if more than one person wants to play!  Help me out...what do YOU do when the weather outside is miserable?