Woody Harrelson said a grown-up is a child with layers on. Doff those pesky layers by embracing organized playtime once again. Across the country, groups like T-Dot Tumblers lead adult trampoline and gymnastics classes to help you take a flying leap from stress. Or, if you’re into reliving your camp days, count down to summer: Tough Mudder is an adult obstacle course. Monkey bars, climbing ropes and rivers of mud recall the myriad joys of gym class, while giving you hysterics and a rockin’ bod.