Mexico's outdoor geography is as varied as its cultural one. The Copper Canyon (Barranca del Cobre) in Chihuahua is four times the volume of the Grand Canyon — a system of six interconnected canyons deeper and wider than Arizona's, accessible by the Chepe railway and by multi-day Rarámuri trail routes into the canyon floor. The Sian Ka'an Biosphere Reserve on the Yucatán Caribbean coast protects mangrove lagoon, coastal reef, and tropical forest in a single UNESCO-designated area where drift snorkelling in ancient Mayan canal channels is a specific experience. The whale shark aggregations off Isla Mujeres from June to September are the world's largest known gathering of the species, accessible on guided boat tours. The cloud forests of Oaxaca's Sierra Juárez deliver mountain biking, hiking to Tule villages, and a winter butterfly migration that rivals Michoacán's monarchs for scale if not fame. Then the hidden gems start showing up. No rush.