Don't pick the wrong volcano: East of Mexico City, the twin volcanoes, Popocatepetl and Ixtacimhuatl, have been enticing hikers for years. And no one had a problem with the 5,452-meter-high Popocatepetl (commonly known as Popo) until it awakened from its 192-year-long slumber in 1994. It's now closed off to hikers. Fortunately, you can still climb sister mountain Ixtacimhuatl (5,286 meters); it's best reached from the town of Amecameca. This is no climb for novices, though: It can be windy, and the temperature is often below freezing year-round. In terms of equipment, you'll need ice crampons; you can rent them in Tlamacas, the staging ground for your ascent. At 3,950 meters, this is a perfect place to acclimatize and serves as a meeting point for climbers. As with any volcano, treat the ascent with caution. And keep in mind the nickname for this mountain: "The Sleeping Woman."