Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

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

This unique building in the main square stands out among the city's typically Baroque architecture.

These temples are among the oldest free-standing stone buildings in the world.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

This prison on the Maltese island of Gozo is almost 500 years old, and they have the graffiti to prove it.

Two geological phenomena in one precarious locale: a towering stone window, and a deep blue void.

The fishing boats that moor in this small lagoon enter and leave through a tunnel to the sea.

The floor of this spectacular Baroque sanctuary is covered in memento mori.

This church is named for one of the most dramatic tales in the early Christian church.

This subterranean necropolis holds three floors of antler-dug grave caves.

These unusual rooms on wheels are holdovers from the 1960s.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

The narrowest house in America is seven feet of pure spite.

Lines from a walking song are etched into a rock in Natural Bridge State Park.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

Rumor has it the hot dog stand was targeted by two Russian nuclear missiles.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

Winding country roads in eastern West Virginia lead to an extraordinary place populated by fiberglass giants.

A massive, majestic mammal watches over pedestrians from his perch atop a former B.P.O.E. lodge.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.