I think everyone has already summed this place up, but here's my 2 cents as well...
First visit to Fort Collins and the first bar we go to is this one and it was awesome. Great atmosphere, very small, but cozy and friendly, it's 103 years old and has the smallest bathroom ever according to the bf.
Don't forget to bring cash since it's "cash only" and be prepared to chill and have some good beer. Happy Hour is 3-8 pm and there are specials along the rear wall, our beers were only $3 each. This is a drinking only place, no food is served which is fine by me. Although cozy, it had seating along the bar, at little tables and bar stools to sit and look out the front window and be a people watcher.
Also, this place has it's own Town Pump Pail Ale by Odell's so we made sure to have one since you can't find it anywhere else and it was a tasty one.
I'll be back next time I'm in Fort Collins.