Ride a boat through this magnificent underground world, which now doubles as a theater.

Built to repay the sins of the father, this church is home to one of the most valuable works of Western art.

This massive subterranean fissure is known as the "underground Grand Canyon."

Christ's blood allegedly preserved in a Belgian town.

The roof of this ancient mausoleum is made from a single Istrian stone weighing a massive 230 tons.

Island wonderland for communist autocrats.

This amazingly well-preserved villa just outside Pompeii boasts rare examples of ancient Roman paintings.

This shining multicolored metro station deep under Naples is said to be the most beautiful in Europe.

Three underground crypts and a pointed arch under the bell tower make this cathedral unique among Romanesque churches.

The remains of the left arm of the levitating philosopher-saint are kept in a 13th-century Neapolitan basilica.

The Neapolitan Cult of the Dead still cares for the skulls at this mini-Fontanelle.

In a city that boasts four separate inclined cable railways, this is one of the busiest funicular lines in the world.

These "anatomical machines" are only one of the many strange items in this Italian crypt.

Pompeii's less famous neighbor is still revealing her secrets.

A fearsome dragon clings to a corner of Munich's city hall.

Geometry and mystery come together in an epic show of octagonal masonry.

An abandoned quarry hides an open-air gallery of huge sculptures, some made from the rubble of 9/11.

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

This 6th-century church has the largest and best-preserved collection of Byzantine mosaics outside Constantinople.

A fossil of a 30 million-year-old fish is unexpectedly hidden thousands of feet above sea level.

Deceased nuns were placed on stone chairs to decompose, while the surviving nuns prayed near the lifeless bodies.

An omelette made with over 1,000 eggs may have been prepared when Holy Roman Emperor Charles V visited this monastery.

High in the clouds of San Marino sits an ancient tower with some curious prisoner graffiti.

A whale rib was used to advertise the store by the arch that offered exotic goods from far away.