An enormous natural sandstone bridge in Kentucky.

Crumbling Kennedys and a decaying Tecumseh are just some of the haunting remains of one man's cement art trail.

More than five miles of underground passageways.

Crumbling ruins mark the site of a couple's grisly murder in the woods.

These ancient ritual mounds are our best window into the culture of the ancient Mississippians.

An abandoned railroad tunnel forgotten by time awaits inquisitive hikers.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

The ruins of the "20-year town" lay out among the mountains of Alberta.

A Nevada mining boomtown that ran out of silver and luck.

This Croatian computer club features such gaming relics as the infamous Virtual Boy and an 8-bit Pacman machine.

The only ancient owl carving found east of the Mississippi.

Ruins of the elaborate house where the enigmatic costume designer threw glamorous parties for New York's theatrical elite.

A scenic canyon with thick forests and historic ruins.

Constant erosion has created a surreal landscape of bleached and preserved fallen trees.

An incredible menagerie of more than 3 million taxidermied animals at the oldest science museum in Europe.

One of the world's largest tanks mimics the experience of watching rare whale sharks, giant rays, and deep sea creatures from the ocean floor.

Crumbling ruins of the thermal baths that once attracted royals and aristocrats from throughout Europe.

No one knows the origins of the mysterious stone ruins discovered on a hillside in Halifax.

This wondrous waterfall rushing down a green-covered mountain wasn't discovered until 2010.

The world's oldest bookshop still in operation.

A petroglyph map of the upper Snake River carved by prehistoric hunter-gatherers.

These beautiful ruins deep in the Pennsylvania woods are thought to have been a ski lodge or a speakeasy, but no one really knows.

An alternate history park where the Union Army loses the war... to dinosaurs.