Hey, If you're looking for a church in Denver to check out before boarding the plane, look into Cathedral Basilica of the Immaculate Conception.
It's the Archdiocese of Denver's "Mother Church" as they call it. I live in Fort Collins, CO which is an hour away from Denver, so I haven't had a chance to go inside. But the pictures look gorgeous. It's where the Archbishop says Mass.
http://www.denvercathedral.org/I think it's near downtown Denver, so probably 30 min drive from the Airport. The airport is in the middle of nowhere.