I'm an investor in Flatiron Athletic Club, so I'm biased. Boulder is a hugely athletic town so there are many great clubs, although almost all of them are now generic national chains. FAC is locally owned (by about 20 high tech and local business people) and run by Keith and Jens - two awesome local entrepreneurs. FAC feels like a local club - lots of non-generic action, the best athletes in town, outstanding trainers that have long tenure, clean and fresh atmosphere - yet not sterile, and continuous small upgrades and changes that are member driver. It's got everything: two pools (indoor and outdoor), weights, treadmill / bikes / spinners, raquetball/squash courts, tennis courts, kids area, yoga, massage, basketball court, and an indoor 1/8th of a mile track (I'm sure I missed something.) It's a "Boulder scene" - everyone is into their workout - don't bother with the spandex - no one is looking at you.