Stone Core Ninja Fitness, Vacaville

If you've ever seen American Ninja Warrior, then you'll understand the sort of exercises you can do at Stone Core Ninja Fitness. But no worries: there are no 15-foot drops into pools here if you lose your grip; instead, the exercises are scaled down so that even an absolute beginner can take part, swinging on hanging rings, climbing up nets, bouncing off trampolines, and more. In the process, you'll get a total-body workout that especially builds upper-body strength, as well as agility. Even kids can try it out with special classes scaled for their developing abilities.