It's so flat where I live that I've done a century with less than 100 feet of elevation gain. Cyclists around here whine about having to ascend the I-10 overpasses. I have to drive to get to hills, and I still need to do a gazillion or so repeats to get decent elevation. In the best of all possible worlds, I'd have a house in Colorado somewhere and fly there for climbing rides.
Alas, I just have to make do.