Elevation gain: 4,934.3 feet Longs Peak Keyhole Route in Colorado is one of the steepest hikes with significant elevation gain, covering about 5,000 feet over a 13-mile round trip.

This 7.2-mile out-and-back hike features a relentless climb with nearly 2,600 feet of elevation gain. This is said to be the most amount of gain you can get on a single trail section in the Catskills.