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

Graffiti-covered ruins that were once part of a farm owned by a mental hospital.

The famous author's birthplace is preserved in a town that he once described as narrow-minded.

What was once one of the country's largest confectionary plants is now an abandoned ruin, but is still pretty sweet.

A display of magnificent stained glass windows is the first exhibit of its kind.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

One of seven Jewish catacombs in Rome and one of only two open to the public.

The underground sanctuary of a mysterious ancient cult.

2300-year-old Roman road connecting the empire.

The museum chronicling a treasure hunter's dream, fulfilled.

This small Key West museum is packed with dozens of artifacts that illustrate the life of the iconic playwright.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

A Roman-style column in Oregon hides a spiral staircase inside.

The unusual patterns in this rock formation result from two distinct modes of weathering.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

A tunnel with windows, so you don't miss out on the impressive views.

Settled by the Church of Jesus Christ of Latter-day Saints in 1859, this abandoned frontier town has appeared in several films.

This stoic, if derpy, giant stands as a monument to Oregon's statehood and the novelty culture of yesteryear.

A 19th-century fortress and collection of artifacts offer a tour of Saudi history.

Ruins of the Crusaders' headquarters.