With more than 200 miles of routes in close proximity to the city, Boulder is a veritable running republic. One local favorite (of recreational runners to ultramarathoners alike!) is the 7-mile Mesa Trail. It connects a huge network of trails that runs beneath and around the iconic towering Flatirons. For an amazing view of the city below, head to the top of the 8,144-foot Green Mountain or 8,461-foot Bear Peak.