ESSENTIALS: A copy of Trails Illustrated's Maroon Bells map ($12; rei.com). Tip: Call the Aspen Ranger District for trail conditions before you leave home (970-925-3445) and stock up on supplies in Glenwood Springs.
PREREQUISITES: Some experience at altitudes above 10,000 feet, moderate fitness; you should be able to jog five miles without stopping before trying the whole circuit.
WHEN TO GO: Mid-September, after the mosquitoes and blackflies have died down and before the swarms of tourists descend to see the aspens change color.