An off-the-beaten path cave with an underground lake.

This little-known relic crypt holds stolen parts of a Roman Empress.

The fading, forgotten remains of a once bright and booming factory.

A neighborhood park in the city of Cáceres hides what some believe are revolutionary examples of Neanderthal cave art.

A corkscrew-shaped barn in Ireland.

Celebrated as a center of civilization, the remains of the ancient city have been nearly destroyed by greed, egoism, and war.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

These 40,000-year-old stenciled hands are older than the famous cave art in France and Spain.

The building features one of the last remaining free-floating spiral grand staircases in the U.S.

The ornate structure is part of a building boasting more marble than the Vatican.

This magnificent mausoleum is as much a work of art as it is a historic resting place.

The roof of this ancient mausoleum is made from a single Istrian stone weighing a massive 230 tons.

An abandoned 18th century manse looks like something out of an Indiana Jones movie.

A locomotive made from 185,000 bricks celebrates the town's pioneering railway history.

Known for the tunnel that leads visitors to the water.

Victorian-era Londoners really wanted to believe this 17th-century cistern was actually an ancient artifact.

A fully functional, 200-year-old remnant of the time when Brixton was mostly fields.

Colorful murals by Jean Cocteau hide within this peaceful London sanctuary.

A monolithic monument in Greater London.

This medieval church tower has maintained its clockworks since the 16th century.

Buried for centuries, this hidden cellar is all that remains of London's medieval Whitefriars Monastery.

This Viking gravestone carved in a rare runic style was dug up from a London churchyard.

A traditional American farmhouse plopped in the middle of a Piccadilly courtyard.

These ornate arches show how the course of the River Thames has changed.