Museu de Arte Contemporanea (MAC)

Designed by the late, legendary modernist architect Oscar Niemeyer, this space-age modern art museum provides a compelling reason to make the half-hour ferry trip across Guanabara Bay to Niteroi. Resembling a giant white flying saucer that seems to jut right out of the mountainside, the building is reason enough to visit and offers spectacular panoramic views across Rio de Janeiro. The exhibitions themselves are often less than spectacular, but the kooky construction is sure to impress kids, as well as adults with even a passing interest in modernist architecture. There's a decent cafe, and entrance to the museum is free on Wednesdays.