The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

The beloved, war-tested mascot of a Union regiment graces their battlefield monument.

A museum dedicated to the history & joys of the trail & your best chance to see hikers throwing up ice cream.

A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

Plaques on its facade commemorate the Tiber's most destructive deluges.

This basilica is dedicated to two saints, one of which is known more for his famous quote.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Nine caves filled with recently-discovered archaeological finds under the houses and the streets of the most ancient district of an old town.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

A copy of the famous statue can be found in this Florence piazza, along with one of the most breathtaking views of the city below.

A slightly creepy gallery of plaster cast models in the same museum as Michelangelo's David.

More than 450 years ago, an Italian nun became the first woman to paint the iconic subject.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

This strange bovine gargoyle is said to have been put in as a passive aggressive form of revenge.

The middle finger of modernity.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

2300-year-old Roman road connecting the empire.

Breathtaking and huge 430 year old maps of Italy.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

The Italian revolutionary's legendary wife is portrayed on horseback waving a gun and holding her child in this memorial on the Janiculum.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.