Sightseeing in Paris, Day 2. Return to Beaubourg.
The outside escalators leading up to the top floor require a 3 euro ticket, which is a rip-off, but the ride is sort of fun. (Of course I had forgotten the cue I got a few years back...)
Also, the building's playful facade makes you want to enter, though once inside there is not that much to do, really, unless you want the museum or the research library.
Currently, an artist named Dale Murdoch is building a sand castle on the first floor, and the shop is always worth a run-through, but otherwise the escalators are truly the best option.