Mexico City is flanked by huge mountains, including the cloud-scraping peaks of 5,230-meter (17,160-foot) Iztaccíhuatl and its neighbor Popocatépetl, an extremely active volcano that's also the country's second-highest peak, at 5,426 meters (17,802 feet). Visible on clear days from the city center, Popocatépetl is more than 3,300 feet taller than the highest peak in the Lower 48, California's Mount Whitney. But Izzi and Popo, as these twins are affectionately known, aren't actually within city limits (they're about 56 to 72 km [35 to 45 miles] south of El Centro). The highest peak within city limits is Mount Ajusco, which is the centerpiece of Parque Nacional Cumbres del Ajusco, the third oldest national park in Mexico. Located in the southwestern corner of CDMX, it's a highly popular destination for hikers. Summiting its 3,930-meter (12,894-foot) peak is no easy feat, however. You'll want to allow at least seven hours to make it up and back, and as trails aren't always well-marked and crime isn't unheard of in this minimally patrolled wilderness, it's best to attempt a hike here with a guide or locals who've done the climb before. At the very least, go with a friend and research online for good trail maps and directions—under no circumstances should you go it alone. The elevation gain from any of the hike's starting points is around 2,500 to 3,000 feet, and it is a steep 10-km (6-mile) round-trip or loop hike (depending on the route), beginning in lush coniferous meadows and rising well above the tree line. You should also be in good shape to make it all the way. But it's a wonderfully rewarding adventure, and the views from the summit of neighboring mountains as well as the entirety of Mexico City to the north are spectacular. An excellent starting point is the trail that leads up from beside the casual Mexican restaurant, Cabaña Mireles La Polea, which is on the north side of the mountain, on the road that encircles it. Uber drivers shouldn't have trouble finding it, and if you drive yourself, you can park at the restaurant (or others near it) if you dine here before or after (the food is quite tasty)—just ask permission first.