I'm an adrenaline junkie and found my love of exercise in biking. You can go fast enough that it's a decent rush, and going out on trails can be really exciting. Once you get into good shape you can hit over 30mph for short times.
You can go even faster with some effort! The other day I was frequently hitting well over 50kph, maxing out around 62kph (30-38mph) and I was trying to conserve energy. It's a hell of a lot of fun. I'm not even that fast or fit - any half decent bike will absolutely fly on a good descent.
