Chasm Lake Trail RMNP is a premier hiking destination in Estes Park, Colorado, covering 8.5 miles with 2400ft of elevation gain. Stats: 8.5 miles, 2400ft gain, Hard. Type: Out-and-Back. Surface: Rock/Dirt. Time: 5-7 hours. Fee: $35 RMNP fee. Dogs: Yes. Permit: No. Wildlife: elk, mule deer, marmots, pikas, black bears, golden eagles, ptarmigan. Best seasons: July through September; carries mandatory reservation through Oct 22; wildflowers peak in August. Chasm Lake sits directly below Longs Peak's Diamond Face — a 1,000-foot sheer granite wall. This dramatic cirque lake at 11,760 feet is one of RMNP's finest destinations without requiring the full Longs summit commitment. 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.