This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

A 1,000-year-old church holds the bones of the Christian martyrs who died hiding inside it.

Medieval torture techniques with a modern conscience.

The Pope’s secret escape route.

A submerged archeological park still holds the wonders of a Roman Sodom.

Deadliest lake in the world suffocated over 1,746 people in one night.

Despite a fraught and controversial history this African island holds a powerful monument to the tragedy of the slave trade.

This tiny, tranquil Senegalese island serves as a powerful symbol of the Atlantic slave trade.

Home of the ruins of a British slave castle.

The Voodoo Superstore of the world.

Where thousands of slaves passed through the "Door of No Return."

Hidden dwellings in the cliffsides of North Togo used by local Moba tribes to evade 18th-century slave traders.

Outdoor exhibits explore the contributions of European, African, and indigenous peoples to American frontier culture.

The Kirkland Monument remembers a selfless Civil War hero who braved the battlefield to give water to his dying enemies.

This statue is dedicated to Grace Sherwood, the last person in Virginia to be convicted of being a witch.

The resting place of a Civil War celebrity's amputated limb.

This once-palatial plantation may have been the site where a draft of the Declaration of Independence was written.

An ancient Viking village in North America that predates Columbus by 500 years.

Caligula's colossal pleasure ships, discovered by Mussolini only to be lost in flames.

This historic recreationist school churns out warriors that may very well have had a fighting chance in Rome's pits of the day.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.