30 minutes on the bike.
I borrowed my brother-in-law's bike and headed for a big muther hill by our house. I just went up and down the whole time to give my legs a workout.
Matt's bike has endured a winter outside so the brakes are pretty squeeky and the chain is rusty. Even with these weaknesses, his bike is in much better shape than mine.
One other problem - the gears don't shift very well (or at all). That wasn't a problem going downhill, but it made going up the hill pretty hard. My legs are mad at me right now.