Far beneath the surface of the water in a cave on Mexico's Yucatan Peninsula sits a magical secret: a spectacular river the flows even underwater.

The following collection has a mix of the longest, deepest, and widest (in area) canyons and gorges from around the world.

Before the days of jetted tubs, spas, and heated pools, the only real place to soak in hot water not in your bath tub was to visit a geothermal hot spring.