What to do in Denver

We get these a lot, so I'll point you to a couple threads that should help out:
http://beeradvocate.com/community/threads/co-breweries-recommendations.25086/
http://beeradvocate.com/community/threads/good-colorado-breweries.20591/
http://beeradvocate.com/community/threads/gabf-advice-brewery-hopping.18129/

In terms of non-beer stuff, you can always take I70 into the mountains. GABF week will be before the ski traffic or snow really kicks in, so it's an easy trek straight up the interstate to reach towns like Idaho Springs, Breckenridge, Frisco, etc.
I'm pretty Rocky Mountain National Park is still open, so that's always a pretty fun trip. You can take I70 up to Winter Park. Grand Lake, through the park, and come back through Lyons or Longmont and hit up one of the Oskar Blues restaurants.

 

You're set on beer related stuff from Domingo's post.

Do you play golf? If so, go play Arrowhead or Fossil Trace (and BM me because I'll be playing at least one of those that week during my vacation). Weather will probably be great that time of year. If you're a sports fan, and depending on when you get in/what GABF sessions you go to, CU plays Arizona State on Thursday Oct 11th up in Boulder. You could hit Avery and The Dark Horse before the game. The Broncos are not in town that weekend, and the Rockies have no hope of being in the playoffs.

 

Two words: Shotgun Willie's.

Seriously though, if the weather is good, go hiking. You can find tons of trails as soon as you hit the foothills. Take some canned beer with you and enjoy the scenery. Even if you don't think you'll like it, I can almost guarantee you will.

 

if you're lazy do mount evans. nice drive, easy drive.

 

If you're going to go that route, La Boheme is across the street from the GABF...and anyone with a ticket gets in for free, too. At least that's what I heard