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

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

The amazing wonder cabinets of a very rich Austrian archbishop.

The largest bell in the world has been swinging high above a Cologne cathedral for almost a century.

One of the ghostly stops along Route 66.

In one of the hottest parts of the Mojave Desert, shallow bedrock forces the typically dry Mojave River to the surface in this canyon, providing a vital oasis for humans and wildlife.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

Don't blink or you'll miss it.

The gambling entrepreneur who built a city was also an avid collector of classic cars.

This once-booming Gold Rush town is now home to a herd of feral donkeys.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

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

The prototype for all Nazi concentration camps.

This statue once earned the distinction as one of the "Three Major Disappointments of the World."

Singapore's oldest Hindu temple.

Singapore's landscaping project is home to 18 incredible Supertrees.

The site of the climactic scene from the classic horror film is now a historic landmark.

Collecting 700 years of mechanical death-dealing, the NRA's sprawling gun museum is a revealing testament to the American obsession with armament.

This train station inspired the name of a 1970's rock band and provided the backdrop for their album cover.

The Aldie Gristmill was once the largest factory of its kind in Loudoun County.

Outsider art meets paleontology at this roadside reptile repository.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

A propulsion engine testbed that paved the way for the Space Shuttle launch sits without recognition at this rocket center.

It may look like no more than a full-scale model, but every part of this full Space Shuttle stack had a working role in aviation history.