The trail heads west into the West Elk Wilderness from Mill Creek Road, Forest Road 727, and the Mill Castle Trailhead. The beginning elevation of the trail is 9,160 feet. It doesn't gain or lose much in elevation until after crossing Mill Creek approximately one and a quarter miles from the trailhead.
Once on the north shore of Mill Creek, the trail begins to climb slowly. It remains close to Mill Creek for five and a half miles and climbs to an elevation of 11,800 feet. The trail forks at this point with the left fork leading to the summit of North Baldy Mountain. (This trail is approximately one and a half miles one way.) The right fork climbs steeply to Storm Pass, 12,460 feet. To continue on the Mill Castle Trail turn north at this fork and climb to Storm Pass. There is a wonderful view of the Castles rock formation from Storm Pass.
The descent from Storm Pass is as steep as the ascent. The trail leads north into the Castle Creek drainage. After crossing to the north shore of South Castle Creek the trail turns eastward and begins to follow the stream. Mill Castle Trail stays close to the stream for approximately a mile and a half, then it begins to lead northward out of the drainage. At this point the Castles are immediately north of the trail.
After leaving South Castle Creek the trail climbs steadily. Within two miles of South Castle Creek it passes two alpine lakes at an elevation of 10,000 feet. At the lakes Mill Castle Trail turns northward. It intersects with Lowline Trail, 438, approximately two miles from the lakes. This is one of the most scenic trails in the West Elk Wilderness. Those interested in obtaining the spectacular views must earn them. It is no easy feat.
Directions from Lowline Trail #438: Mill Castle Trail is also accessible by Traveling south on the Lowline Trail #438.
Directions from Beckwith Pass Trail, 840: Trail 450 can be reached via Beckwith Pass Trail and Lowline Trail. Access to these can be gained from Lost Lake Campground.
Directions from Mill Castle Trailhead: The trail leads west from Mill Castle Trailhead, which lies four and a half miles west of Ohio Creek Road on Mill Creek Road.