More than 150 years after it became the world's first national park, Yellowstone still draws millions each year to witness a landscape unlike any other on Earth. The reason lies beneath their feet: a massive volcanic system that powers the greatest concentration of geysers on the planet.

Old Faithful remains the headliner, erupting roughly every ninety minutes with a plume of scalding water that can top a hundred feet. Its reliability made it famous, but it is only one of hundreds of geysers scattered across the park's basins, each with its own rhythm and personality.

The geysers are just the beginning of the park's thermal wonders. Bubbling mud pots, hissing fumaroles, and terraces of mineral-laden hot springs create an alien world of color and steam, a constant reminder of the immense heat churning below.

Visitors are warned, repeatedly and for good reason, to stay on the boardwalks. The thin crust over these features hides pools hot enough to be deadly, and the ground that looks solid may not be. Treated with respect, Yellowstone offers a window into the raw power of the planet, a place where the Earth's inner workings rise steaming into the open air for anyone to see.