The City Museum of St. Louis is an entire building's worth of a playground.  The building is outfitted with archaic media such as artwork, but is truly a giant playground for children and adults to explore.  There are slides and secret passages everywhere, and themed areas like a miniature amusement park.  A series of underground caverns with "dinosaurs", a large treehouse with passages everywhere, a tunnel beneath tastefully decorated aquariums and running water, a funhouse of games and arcades and a room of mirrors are the least of the many installations inside this "museum", which all blend seamlessly into one giant playground of an installation.  The building itself is a massive playground for all ages.