The options are as overwhelming as the peaks. Allow us to simplify. (1) The Classic: Everest Base Camp. According to RMI guide Melissa Arnot, the first Western woman to summit Everest three times, "you won't find overcrowded trails (unless the yak trains are considered crowding). The Khumbu Valley contains some of the most unique culture of anywhere I've ever been. The trek, which can take up to three weeks, is moderately challenging. Fall is optimal for cool, crisp weather, but if you want to witness the summit stampede, go in spring, when most Everest expeditions start." Arnot guides the Base Camp trek for RMI ($4,500; rmiguides.com) and offers customized trips through her company, Infinity Expeditions (from $3,000; infinityexpeditions.com). (2) The New Trip: It's not complete, but the Great Himalaya Trail will stretch a total of 2,800 miles through China, Bhutan, Nepal, India, and Pakistan. The Nepal section alone covers more than 1,000 miles at altitudes from 7,800 to nearly 20,000 feet. The first company to guide commercial treks on the trail will be World Expeditions (starting in February 2011, from $3,600; worldexpeditions.com).