Gym Runs on Runs
The California Fitness center in Hong Kong has outfitted its exercise machines to convert the work from sweating patrons into electricity that powers the gym's lights.
Ninety percent of the energy generated by stair-stepping legs had previously dissipated as heat.
Ideas like this are so brilliant and so obvious it's almost embarrassing when they're finally executed.
Imagine a competitor introducing the same machines and paying patrons a slice of the money they save the gym during their workout sessions.