Concrete floors and rusty bars don’t seem like the ideal workout space, especially compared to a spacious, fully equipped gym. Yet, the urban environment has inspired a new breed of training. It’s usually called “the prison workout,” but is also sometimes known as “convict conditioning” or simply “bodyweight strength training.” It’s a great workout for someone who needs action, but is bored at the gym. Instead, the focus is internal and only occasionally relies on scaffolding, city parks, or parking meters for the bare equipment needs. Because of the minimalistic approach, it’s also one of the greenest workouts around.