Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

Human-made caves excavated to hide a secret society of wealthy pagans.

This Italian-style temple replica has been threatening to fall off the Irish coast for hundreds of years.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

A lover's walk between hilltop towns, decorated with graffiti love notes.

A cave network located at the southernmost tip of mainland Greece was once believed to be an entrance to Hades.

These delicate ruins need more tourists to keep them from fading away.

A formerly abandoned mental institute, now back in business.

The second-largest (of only two in the world) large particle collider is the underdog of experimental physics.

An unrealized dream to wirelessly electrify the entire Earth.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

The end of the 4 Line is also the end of the line for 300,000 souls in one of NYC's most illustrious cemeteries.

Little Red Lighthouse under the George Washington Bridge.

The highest point on the island known for buildings that touch the sky.