Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

The site of Paul Revere's historic two lantern warning.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

Erotic art covers the walls of the largest ancient pleasure palace.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

Pilgrimage site for star-crossed lovers.

2300-year-old Roman road connecting the empire.

The yawning maw of this pagan visage is said to bite off the hands of liars.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

Historic medieval fortified city in southwest France.

A Gothic cathedral created from volcanic rocks.

Ancient paintings known as the "Sistine Chapel of Cave Art."

France's most famous cemetery, with some of its most curious tombs.

A castle from the Holy Roman Empire that hosts traveling youth... in its stables.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

This historic stone bridge has an entire neighborhood clinging to its sides.

A sprawling Baroque park with 300-year-old hydro-pneumatic waterworks.

The fairy tale castle of the "fairy-tale king."

A serious museum dedicated to two German comedians.

This former steel and coal plant is now a neon-lit industrial fantasia.

This historic stone gate tower is now just a lonely relic in the middle of a swamp.

A marvel of Byzantine engineering under the streets of Istanbul.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.