WUAH! Walk Up All Hills.
Well, maybe not all of them, but works for me. I'm not out to be super competitive, or accomplishment oriented. I like the change of pace.
The mechanical advantages of a bike are great on the downhill side, but they work against you on the uphill side. Walking is a more sophisticated way of going up a hill. (as I see it)
It gets a bit of variety into your exercise, and I find it pleasant.