Once the home of a hermetic monk, this cave now houses a small church.

The most famous location in China was home to whole dynasties worth of imperial rulers.

One of seven Jewish catacombs in Rome and one of only two open to the public.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Abandoned railway line circling the city of Paris.

This odd California folly seems like it was almost designed to accumulate urban legends.

A World War II officers' club features Old West murals painted by German POWs.

A little stop along the Texas highway where Rock Hudson, Elizabeth Taylor, and James Dean stayed while shooting the 1955 film "Giant."

With print dying, this local paper keeps the lights on by doubling as a stunning cafe and cocktail bar.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

The world's oldest and largest museum of mass transit vehicles.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

An ancient octagonal weather station named for the eight Greek gods of wind.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

This legendary city has been a tourist attraction for centuries.

The ruins of an abandoned medieval city where the last Byzantine emperor was crowned.

The historic tower houses of this nearly abandoned Greek town have been compared to the spikes on an iguana's back.

Large collection from the 3rd millennium BCE.

This town named for the ancient God of War is home to fewer than a thousand people, but it's the birthplace of the Greek Revolution.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

Sparkling, calcite-covered skeletons of children who may have been sacrificed to appease an angry god.

One of the most enjoyable bits of history at Coney Island and “the most romantic ride in the world.”

An emerald-green grotto just a short trip from Austin.

The remains of a failed subway in upstate New York is now an underground graffiti bunker.