Mountaineers Route is the original and easiest way to reach the main summit. It was first climbed by John Muir himself in 1869, and was a significant achievement in American alpinism at the time. Most of the route is a steep hike and scramble on dirt and rock slabs, but the summit spire requires about 20 feet of Class 4 rock climbing, using cracks and blocks for hand and footholds.

A rope and trad gear are recommended for this route. Experienced climbers can go without the gear, but a rope still makes the descent easier and safer. The climbing is not hard, but it is steep enough that a fall could be deadly. You can rappel or lower on belay from the summit block, then rappel at least once more during the descent to avoid downclimbing the whole way.

The approach is from Cathedral Lakes Trailhead. Follow the John Muir Trail south for a short bit before turning on an unmarked but well-traveled climber trail along the creek. The trail traces the creek for a while before turning steeply uphill toward the Southeast Buttress of Cathedral.

The Southeast Buttress, a sweeping curtain of fine granite, is the classic rock climbing route. Mountaineers Route takes the sandy, treed slope to the right of it to gain the north ridge. At the ridge, cross to the west side by downclimbing through a notch. Traverse south on Class 3 slabs on this west side. Before quite reaching the west ridge, head up toward west face of the summit. Once standing at the base of the summit block, traverse around to the south side to find the easiest way through. Follow one of two short, Class 4 crack systems to the summit.

From the narrow perch atop Cathedral Peak, the view is phenomenal. As far as you can see are sculptures of granite, pools of blue water, carpets of green in between, and peaks of the Sierra on the horizon. Return by rappelling and/or downclimbing then retracing your steps down the trail.

Sources: https://www.summitpost.org/cathedral-peak/150524 https://www.summitpost.org/mountaineers-route/155736