Hiking

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.

Booth Lake. This is one of Vail's most popular hikes, so get on the trail early or pick a weekday during the summer high season. It's a sustained 4-mile one-way climb with more than 3,000 feet in elevation gain to Booth Lake at 11,500 feet, right above the tree line. Fit hikers can do this in about seven hours. En route, you can cool off at the 60-foot waterfall; at only 2 miles in, this is also a great spot to turn around if you're seeking 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., Vail, Colorado, 81658.

Eagle's Loop. This trail starts from atop the Eagle Bahn Gondola at 10,350 feet, but it's a mellow, 1-mile stroll along the mountaintop ridge with panoramic views of the Mount of the Holy Cross. Allow about half an hour. A one-day lift ticket for the 14-minute gondola ride is $39 for adults. Adventurous types may prefer to skip the gondola (and the fee) and hike the intermediate, often steep, 4½-mile trail through aspen trees and wildflowers to the beginning of the Eagle Loop trail. Trailhead: Top of Eagle Bahn Gondola, Vail, Colorado, 81657.

Outfitters and Expeditions

Paragon Guides. In summer, hiking with llamas is a highlight of this backcountry adventure company's offerings. Llamas carry food, wine, and water on lunch hikes or wine and cheese excursions, and help with overnight packs on hut trips. Paragon Guides also offer rock climbing, mountain biking, and fly-fishing trips in and around Vail Valley. 210 Edwards Village Blvd. , Edwards, Colorado, 81632. 970/926–5299; www.paragonguides.com.