Best Hiking Outside of Denver?

South of Denver is Waterton Canyon (6.5 mile up and back on gravel road for hike, walk / run, mountain bike, etc. w/ more technical trail system at the 6.5 mile mark to extend) and Daniels Park Rd (gravel road for hike, walk / run, mountain bike, etc. - gorgeous views of Pike's Peak, etc.) - hope this helps...

Hey bud, head over to Red Rocks Amphitheatre (Morrison, CO) about 30 minutes west of downtown Denver. Some great hikes around there. The further west you go from there, the better available hiking (deeper into the Rocky Mountains). Other options: If you don't mind an hour drive, head south to Colorado Springs where you can check out The Incline (famous amongst the potential Olympians at the training center down there - don't worry though, you don't have to run it). If you're looking for a real climb, CO has 52 fourteeners (mountains over 14,000 ft.), some of which are quite manageable, simply long hikes.

There are some great trails at Castlewood Canyon State Park, and without a huge elevation change, in case you aren't quite acclimated to the elevation. 

The Mount Sanitas Trailhead is a little more of a workout, but leads to great views that stretch from Boulder back to Denver and beyond on a clear day. 

Alderfer/Three Sisters Park in Evergreen is about 45 minutes west of town, but will get you up into the foothills and some great views on a fun trail. 

There are some beautiful trails around Nederland, although they can get crowded. Head north for a hike at Devil's Backbone in Loveland (Colorado). Super unique scenery. Make it longer and walk all the way to Fort Collins via this trail's connectors.