The medieval network of canals hidden underneath the city is opened to explorers each year.

These 12th-century catacombs carved into a mountainside were a place of mysticism and Christian hermitages.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

This small Bavarian graveyard is filled with empty graves for German soldiers lost during the World Wars.

The prototype for all Nazi concentration camps.

This magnificent museum claims to house the cranium of a disciple and the skull of a pope.

The patron saint of spinsters grasps a container of dried blood.

Daily jousts and dancing barrel makers in Munich's mechanical clock.

A fearsome dragon clings to a corner of Munich's city hall.

The footprint of a frustrated devil in Munich's Cathedral.

Babe Ruth and others planted saplings for a 1930s tourism campaign. The saplings grew as the area faded.

The colonial home of Paul Revere during the American Revolution.

This grove was planted more than a century ago by the War Mothers of World War I.

The final resting place of an iconic drag performer is decorated with pearls and hot-pink lipstick.

On the outskirts of Pennsylvania’s capital city, a reminder of the worst accident in U.S. commercial nuclear power plant history.

Home to a vast and influential collection of Shakespeareana.

The final resting place of the tragic king and queen of the Jazz Age is tucked away in a small Maryland graveyard.

This small cemetery remains hidden behind a recreation center.

Once part of an extensive network of fire towers, this is one of the few remaining in this Wisconsin forest.

Wisconsin's most celebrated export gets the royal treatment on I-94.

Born a slave on the Arlington estate, Parks dug the first graves at Arlington National Cemetery, and was buried there, too.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

Engraved in stone here are the signatures of everyone who signed the Declaration of Independence.

Take a step into the workshop where Edison and his employees revolutionized the world.