Mills Lake Trail RMNP is a premier hiking destination in Estes Park, Colorado, covering 5.6 miles with 700ft of elevation gain. Stats: 5.6 miles, 700ft gain, Moderate. Type: Out-and-Back. Surface: Dirt/Rock. Time: 3-4 hours. Fee: $35 RMNP fee. Dogs: Yes. Permit: No. Wildlife: elk, mule deer, marmots, pikas, golden eagles, American dippers. Best seasons: July through September for best conditions; one of RMNP's most photographed mountain lake views. Mills Lake frames Longs Peak, Keyboard of the Winds, and the Cathedral Wall in a classic Front Range alpine view. Named for Rocky Mountain NP's co-founder Enos Mills, this moderate hike rewards with one of Colorado's most iconic mountain lake panoramas. Pack plenty of water — desert and high-altitude trails demand more hydration than you expect. Layers are essential above 10,000 feet. Leave No Trace: stay on designated trails, pack out all waste, and respect wildlife and other visitors.