Castle Mountain is a mountain located within Banff National Park in the Canadian Rockies, approximately halfway between Banff and Lake Louise. It is the easternmost mountain of the Main Ranges in the Bow Valley and sits astride the Castle Mountain Fault which has thrust older sedimentary and metamorphic rocks forming the upper part of the mountain over the younger rocks forming its base.
The mountain's castellated, or castle-like, appearance is a result of erosive processes acting at different rates on the peak's alternating layers of softer shale and harder limestone, dolomite and quartzite.
While the peak presents a formidable challenge to climb when viewed from the highway, the mountain can be ascended by first hiking to Rockbound Lake which is located on the easier backside. A break in a cliff band provides access to a route above the lake. The ascent is a very long day when undertaken from the trailhead and can easily require 12 hours for a return trip.