Hi Country Stables. Guided horseback rides in Rocky Mountain National Park. From $40 per person for two hours. Two locations: Glacier Creek (970/586-3244) and Moraine Park (970/586-2327).
Maroon Bells-Snowmass Wilderness Area. 100 miles of trails and dozens of peaks (including Castle) in Gunnison and White River National Forests. Free wilderness permit required to hike Maroon Bells; available from U.S. Forest Service (806 W. Hallam Ave., Aspen; 970/925-3445) and at trailheads.
Aspen Expeditions. One-day rock-climbing trips and guided mountain ascents from $150 per person. 426 S. Spring St., Aspen; www.aspenexpeditions.comwww.aspenexpeditions.com or 970/925-7625.
Crested Butte Mountain Bike Trails. Pick up a free trail map at visitor center, bike shop, or the Mountain Bike Hall of Fame (12-7 daily; 331 Elk Ave., Crested Butte; 800/454-4505).