This is "MonstroCity" at the City Museum here in St. Louis.  It is a huge suspended maze of random architecture that you can walk, crawl, climb, and slide your way through.  It was definitely built with adults in mind, because all but a very few little parts of it are nicely sized for adult adventurers.  As you can (kind of) see, there is a firetruck, a big crane, and two smaller airplanes all built in.  It is amazingly awesome and fun to play in!  If any of you come to visit here in St. Louis, make sure this is a part of your trip!  Oh, and bonus for those of you who would prefer to explore such an attraction with minimal children around, the City Museum is open until 1am on Friday and Saturday nights, and there’s a little bar/cafe on the ground floor that opens in the evenings as well.