This was a must-visit on my recent trip to St. Louis. If you ever find yourself in St. Louis, please do yourself a favour and go here. It is a crazy jungle gym play place that looks like it is straight out of a children's storybook. Pretty much anything you could climb on or through, you can. There is a cave area with tunnels through the walls, a rainforest area with a sturdy wire mesh canopy to climb around on, a crazy outdoor play area with wire tunnels suspended fifty feet in the air to climb through, slides that are multiple stories tall and you have no idea where they might come out, as well as an entire rooftop area that was unfortunately closed when we were there because it was a tad drizzly out. You could easily visit here four or five times and still not explore every nook and cranny in this insane museum.
A little tip, make sure you wear good climbing clothes! Long pants to cover your knees and some comfy shoes are a must.