I've only been riding a few months on a hybrid so take this for what it's worth. I live and ride in a fairly hilly area with some good climbs. And I thought that was good training for building endurance. But I recently went on vacation down on the Eastern Shore and rode on perfectly flat terrain. I was thinking it was going to be easy, but I think it may have been harder! The difference being that instead of being able to coast along on descents, I was pedaling the entire friggin time. Is my perception correct, or did I just have a bad ride?
Also, flat rides are boring. No fast downhills. Felt like I was in a cycle class just pedaling away.