The Mile High City is one of the best outdoor cities in the US, bar none. The culture alone is rooted in camping and the outdoors, and you can find all the adventure you can handle in this section of Colorado.
Denver is the gateway to Rocky Mountain National Park as well as more USFS and BLM land than you’ll know what to do within three lifetimes. The best camping near Denver is easily in Rocky Mountain National Park, though tent and RV campsites go fast due to its popularity. If you can’t get a campground, try the Mount Evans Wilderness area or any USFS land in the Breckenridge, CO area.