I lived there for 6 years (deployed 2 of those) and really loved living out there. We moved at the end of 2006.
If you are active, it has to be one of the best places to lived. You are about 2 hours from skiing, but it is 2hours to world class skiing. COS sits against the Rockies, so the mountains are right there. 5min after leaving work you can be in the mountains riding/running very, very good single track or climbing quality rock.
I did not weightlift while I lived there. But, USAW is headquartered there, as well at the OTC, so I am sure there is an underground scene.
Fountain sits on the southeast side of town. It is just east of Ft. Carson, a large Army base. From Fountain, you are about 25min to trailheads. Also, if you want the moutains, look at Woodland Park. It is about 20min west of COS, sits at about 8500ft. The homes there are pretty well priced and it is a mountain town.
I have heard the city has gone to pot with the economic downturn. The housing market seriously crashed and the city is running out of money. They are closing parks, not picking up trash, etc. My biggest complaint about the city was that they did not plow the snow enough.
But, all in all, I loved living there. Good luck.