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

Dress up like a miner and take a slide into the disco-lit depths of this once foundational salt mine.

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

The prototype for all Nazi concentration camps.

Daily jousts and dancing barrel makers in Munich's mechanical clock.

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

Narrowest house in Boston.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

St Bernard de Clairvaux Episcopal Church, better known as one of the oldest European buildings in the Western Hemisphere.

A Circus legend leaves an unexpected endowment.

A haunted hill that supposedly defied gravity.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

A building so large that it has its own weather.

Electrical pylon in the shape of Disney's beloved mouse.

Welcome to old Florida, where a 1940s mermaid show is still enchanting visitors.

Location of a reliquary containing bone fragments of 18 saints.

Intertwined, interspecies trees which locals believe can grant boons to lovers.

An ancient knight and a symbol of the city's freedom.

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

A "miracle" that seems to produce more holy fistfights than holy revelations.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Go inside to really appreciate this 500-year-old technological masterpiece.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The final resting place of the poets Shelley and Keats.