Replying to Coolest place to camp within a days drive of Colorado?

I've been looking around for good ideas for a place to camp around the colorado, utah, arizona, texas etc.. area and having trouble picking just one place for me and some friends to go for 3-5 days. we're starting from my friends place in denver, could really go anywhere within a days drive. anyone got some ideas for placest to check out? can be either hike to or car camping, a place to swim could be nice, the less people the better, we're pretty open to ideas.