Hiking in Vail

If you aren't used to it, high altitude can catch you off guard. Drink plenty of water to help stave off the effects of altitude sickness—dizziness, shortness of breath, headache, and nausea. Slather on the sunscreen—it's easy to get sunburned up here. And, in summer, an early morning start is best, as afternoon thunderstorms are frequent and a danger above the tree line.

Eagle's Loop (Trailhead: Top of Eagle Bahn Gondola) starts at 10,350 feet, but it's a mellow, 1-mi stroll along the mountaintop ridge with panoramic views of the Mount of the Holy Cross. Allow about half an hour.

Booth Lake is one of Vail's most popular hikes, so get on the trail early or pick a weekday during the summer high season. This is a sustained 6-mi one-way climb from 8,400 feet to Booth Lake at 11,500 feet, right above the tree line. Fit hikers can do this in about seven hours. En route, hikers can cool off at the 60-foot Booth Creek Falls; at only 2 mi in, this is also a great spot to turn around if you're feeling winded (this should take about two to three hours round-trip and is a great option for an easier hike). The reward for pushing on is a nice view of Booth Lake cradled among the alpine tundra. Trailhead: Take Exit 180 from I-70 to end of Booth Falls Rd.

Paragon Guides (Box 130, Vail, 81618. 970/926-5299. www.paragonguides.com) offers backcountry adventures. In summer, there's rock climbing, mountain biking, and day and overnight llama treks in and around Vail Valley. In winter, the company runs daylong ski trips through the backcountry, and three- to six-day trips along the 10th Mountain Division Hut System.

The Holy Cross Wilderness Area is southwest of Beaver Creek. Eagle Lake is a great trail for hikers who want to test their bodies out at altitude without overdoing it. The trail starts at 9,100 feet (just slightly higher than Beaver Creek's base at 7,400 feet) and contours through a glacial valley for almost 2.5 mi around Woods Lake to Eagle Lake at 10,000 feet. Plan on a five-hour round-trip journey. You can continue up the valley to explore more lakes if you're feeling fit. Holy Cross Ranger District, White River National Forest. 970/827-5715. www.fs.fed.us/r2/whiteriver/recreation/wilderness/holycross.

The Beaver Creek Hiking Center (Beaver Creek Village. 970/754-5373) arranges everything from easy walks to difficult hikes. If you're traveling with kids, ask about educational programs.