I've been riding my bike for at least a year and at first it was hard, but its gotten easier(in fact too easy) and I don't even break a sweat taking a ride, even if I go pretty fast. I can't switch gears on my bike, and in my town the ground is flat everywhere, so how can I make a bike ride more challenging, or at least interesting? There are only 2 neighborhoods I ride my bike in because I'm 15 and I can't really go anywhere, lol.