Yellowstone, United States

Yellowstone, the world's first national park, proves that volcanic fury can create beauty: its 500 active geysers — more than all other global geothermal areas combined — erupt across 2.2 million acres. The park's supervolcano caldera measures 72 kilometers across, and the Lamar Valley teems with wild bison (over 4,000) and 10 wolf packs in winter. With over 1,000 species of plants and 67 species of mammals, Yellowstone's ecological variety is second to none. Its 1,770-kilometer road network makes this geothermal wonderland accessible, yet 99% of visitors never venture more than a mile from their car, leaving the 20,000 square kilometers of backcountry for those who seek true solitude.