The Baldpate Inn, near Estes Park, boasts the world's largest key collection. It's worth the 7-mile trip, if you happen to be in Estes.
They have keys from Edgar Allen Poe's college dorm room, keys to almost uncountable numbers of cities - and more. Most of the keys are from at least 30 years ago. (If it was the world's largest collection then, why add more?) And besides, the room is pretty full.
Interestingly, the Inn is only open from May through October. The snow just gets too deep.