Castle Peak is a fourteener in the Elk Mountains of the US state of Colorado. It is the highest peak in the Elks and the twelfth highest peak in Colorado. The peak rises along the Pitkin-Gunnison county line, approximately 15 miles (24 km) south of Aspen. The best climbing months are June, July, August, September through the Montezuma Glacier, a permanent snowfield between Castle and Conundrum Peaks. There are two standard routes for ascent. The Northwest Ridge features a moderate snow climb followed by an easy ridge scramble. It should not be attempted late in the summer, when the of loose dirt and scree meet the climber near the top of the Castle-Conundrum saddle. The Northeast Ridge features an easy snow climb, but slightly harder scrambling and route-finding once on the ridge.
Conundrum Peak is a northern subsummit of Castle Peak. It has two closely spaced summits; the northern is higher, with elevation 14,040+ ft (4,279 m). It is 0.4 mi (0.6 km) north of Castle Peak, and has between 200 and of topographic prominence. This does not meet the usual 300 foot prominence criterion for an officially separate peak; however it is often climbed in conjunction with Castle Peak.