Yep, get a real bike. Where in the country are you? There are bound to be some excellent cycle routes.
Last weekend I headed out to the Peak District with a few friends and we defeated Winnats Pass (I say defeated, most of us survived going down it - only one of us turned around and went up it as well) - amazing stuff and impossibly good for you.
A decent road bike only costs around £500 and is a mode of free transport forever! Well worth it, even if, eventually, you only use it to pitch yourself down at the pub and back.
Spare Ed