Queeny Park in St. Louis has a very unique playground. It was built in 1974 and reminded me Super Mario Bros when I saw my kids popping up out of tunnels. The surface of almost the entire playground is pea gravel, so this is definitely not a place to wear sandals.
The park has two entrances. You'll want to use the Weidman Rd entrance to access the playground. There's a portable restroom next to the playground, but it has no lock.