The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

St. Augustine's record-setting narrow street was designed to protect against pirates.

This Big Sur waterfall drops 80 feet directly into the Pacific Ocean, and inspired the hillside house up top.

What was once the largest NFL stadium.

This quirky hot springs town known to locals as "T or C" was named after a radio show.

Crumbling remnants of what was once a booming town full of silver.

These ruins of a pre-Columbian cliff village are among the most beautiful and well preserved in New Mexico.

This is one really big nut.

Twenty-seven massive radio antennas on the high plains of New Mexico search for life on other planets.

A multi-storied adobe complex has been inhabited for more than a thousand years.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Public works and national defense project meant to carve a canal all the way across the state of Florida.

A luxurious 1880s hotel with its fair share of Tiffany stained glass, Edison electricity, and of course, ghosts.

An 18th-century Spanish watchtower made entirely of seashell and concrete.

The third tallest lighthouse in America once guided author Stephen Crane to safety.

The ruins of this antebellum sugar plantation are the end result of a Seminole attack during the Florida Wars of 1836.