Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

These delicate buggers are some of the rarest fossils that have bubbled up from the Tar Pits.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

The angel of death appears to weep black tears at this grave marker.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

This strange seaside tower got its name from a wealthy eccentric who would hide coins among its stones.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

The largest self-built castle in the U.S., six decades in the making.

A modernist landscape of water and sci-fi concrete.

This geothermal hot spring hides beneath a slowly growing mineral dome.

The world's longest known cave system.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A replica that won't float away.

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

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

This naturally-sourced hot spring is now home to a clothing-optional resort.

Take a drunken tour inside the world's largest known geode.

Odd outsider art installations surround a Gold Rush-era ghost town.

Where beautiful signs live on forever.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.

Towering basalt columns, a creation of fire and ice.

Crypt mausoleum in cathedral's basement contains relics of third century Roman martyr, Saint Vibiana.