The collar worn by a fourth-century saint resides in this church, and is still used for blessings to this day.

A large statue of Pope Gregory XIII in Bologna was disguised as Saint Petronius to avoid destruction.

Legend has it this fountain built to symbolize the Pope’s power hides a strange secret concerning Neptune's manliness.

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.

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

The remains of this 2nd-century Roman temple are incorporated into a modern building.

This ancient market is often referred to as the oldest shopping mall in the world.

Ancient ruins hidden underneath a modern luxury hotel.

A magnificent waterfall is also home to the remains of a Roman hydraulic engineering system.

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

Jesus' footprints and the first catacombs in the world.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

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

This colorful gate stands as an entrance to the walled city of Old San Juan.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

A marvel of Byzantine engineering under the streets of Istanbul.

The (usually) serene burial place of the world's most notorious drug lord.

An unusual and beautiful form of mass transit serves the city's steepest neighborhoods.

Outdoor escalators and art have helped change what was once a notoriously dangerous part of Medellín.

Home to 23 voluptuous and instantly lovable sculptures by one of Latin America's most celebrated artists.

Two identical statues by Fernando Botero, one blown to pieces in a terrorist bombing, the other donated as a gift for peace.