If mountain bikes are your thing, you'll find plenty of dirt roads and backcountry pathways to explore. Many national parks and forests have a good selection of trails--Acadia National Park's carriage roads, for example, are unique. You can also take guided tours through 60 miles of connected trails in the Sebago Lake area, near the New Hampshire border, with Back Country Excursions (tel. 207/625-8189), which operates a mountain-biking playground called the "Palace" in Limerick, Maine.

Out in Colorado, ski areas often open their lifts to bikers in the summer. Winter Park is considered the state's mountain-bike capital (tel. 800/903-PARK or 970/726-4118). The state's single best route, the 30-mile Tipperary Creek Trail, ends at Winter Park.

In Deschutes National Forest, outside the town of Bend in central Oregon, dry ponderosa pine forests are laced with trails past lakes, waterfalls, and great views of the surrounding mountains. Contact the Bend/Fort Rock Ranger Station (tel. 541/388-5664). Another popular area is the Bryce, Zion, and Canyonlands regions of southern Utah. Contact Rim Tours (tel. 800/626-7335) or Kaibab Mountain Bike Tours (tel. 800/451-1133), based in the town of Moab.