could do bug obstacle course DIY American Ninja Warrior Backyard Obstacle Course - Five different elements. Build and re-build this obstacle course, and then it breaks down for storage. Storage ideas in the post.
How to Build Your Own American Ninja Warrior Training Course
This is a pretty amazing playground! It's a part of a HUGE obstacle course for children, called the Heiwa no Mori Koen Field Athletic Course, in Tokyo. I love the challenge and the sense of risk. I'm sure plenty of children get wet :)