Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

The world's longest known cave system.

Where manatees are the snowbird vacationers in these balmy Florida springs.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

A beautiful geyser under environmental threat.

This abandoned amusement park was built on a site with a dark history.

The first declared National Monument in the United States.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

Enormous lake at the bottom of a unique cave system.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

Most-visited and most-photographed slot canyon in the American Southwest.