The route described here is for Castle Peak alone, not the linkup. The mapped track begins from the Castle Creek Trailhead, but capable vehicles can drive much of the way on a 4WD road. This road leads up into Montezuma Basin, above treeline at the northeast foot of Castle and Conundrum Peaks.

The road ends at a small flat spot in the center of the basin at 12,800 feet, where steep talus and snowfields arise on three sides. Castle and Conundrum Peaks tower overhead. The trail to Castle leads straight up a talus slope then traverses beneath an imposing, craggy subpeak that guards the main ridgeline. Expect to cross snow on this section, especially in early season.

Then the trail, which is visibly worn into the slope, takes a few switchbacks before making an arcing traverse up to the spine of the mountain’s northeast ridge. As you climb, views open up of the high basin below the two peaks, and an icy little lake within it.

The route becomes more engaging once you gain the ridgeline. You’ll negotiate large boulders and short vertical sections as you work your way along the spine. Nothing should be much more difficult than Class 2, though, if you remain on route. You’ll occasionally veer to the right around obstacles, but not too far. Don’t drop down any gullies, just stick to traversing beneath or climbing over low cliff bands on the crest.

The terrain eases up atop a small false summit, within 400 feet and an excellent vantage of the true summit. From there, drop to a notch through some short scrambles. Be especially wary of your footing here. The final stretch to the summit is on brittle and loose rock, but it's safe enough if you are careful. Wade through a steep but short section of scree to reach the summit.

After taking in the view from highest mountain in the Elks, descend the way you came. In early season there is usually enough snow in the couloirs to glissade the descent to the upper basin with the lake, and maybe farther. Attempt this only if you have the proper gear and experience, and if snow conditions are safe.

Sources: https://www.summitpost.org/castle-peak/150482 https://www.14ers.com/route.php?route=cast1&peak=Castle+Peak+and+Conundrum+Peak