An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.

A flooded Mexican cave that hides a river beneath the water.

A sprawling network of century-old subterranean catacombs lies beneath a nondescript suburban home.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

This popular cave pool is truly magical, despite the crowds.

Found down a long dirt road, a sacred Mexican cenote and 18th-century hacienda remain hidden.

These azure waters were thought to lead to the Mayan Underworld.

According to legend, this hacienda was abandoned because of a curse.

A magical sinkhole on the Yucatán Peninsula is adorned with mini waterfalls and hanging vines.

Three sinkholes filled with warm, crystal-clear water reached by a horse-driven cart on an old train track through the jungle.

Take a dip beneath the stalactites in this amazing cenote.

One of the few places where you can visit a cenote and Maya ruins at the same time.

An elaborate Mayan city shrouded in alien conspiracy revealed the tomb of Pacal the Great.

Three small rooms in the jungle house the most elaborate and intact murals of the Mayan world.

The striking jade death mask of an ancient Maya king is displayed in a replica tomb in Mexico City.

This small museum tucked within a subway station holds pieces from Madrid's past.

Abandoned since the 1950s, the streetcar lane beneath the heavily trafficked bridge lays empty and unused.

A wondrous old library overlooking the nation's capital.

A derelict bit of transportation infrastructure hidden in the woods.

Home to the abandoned Tioronda Hat Works Factory, this park is a combination of woodlands and marshlands.

A granite rock formation littered with various species of moss, lichen, and fern.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

Abandoned ships along a deserted beach feel like the set of a post-apocalyptic thriller.

The remains of the worst maritime disaster in the history of the "Graveyard of the Pacific."