Collapsing castle on the Hudson river was once the storage site of military surplus business.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

The world’s oldest and biggest bookstore stocking only mystery, crime fiction, espionage, and thrillers.

New York's oldest magic store.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

A crumbling hospital from the 1850s on Roosevelt Island.

A terrific purveyor of natural history objects and curios.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

An otherworldly restaurant perched on the edge of a jagged cliff next to a medieval holy city.

Named for the biblical warrior, the largest castle in Israel actually dates to the Middle Ages.

This Aztec structure remained hidden until the demolition of a supermarket exposed the lost temple.

Zurich's evolution museum hosts a unique collection of skeletons among its natural history treasures.

The abandoned medieval theme park was meant to be the "Disneyland of the Philippines."

It was an experiment to prove that glacial boulders and rocks can be used in constructions and dwelling.

You can row a boat through this ancient underground reservoir.

Arguing within this idyllic, circular volcanic lake is forbidden.

Once part of an ancient international harbor, it's now an all-you-can-eat shrimp buffet for flamingos and other water birds.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

This 15th-century Serbian Orthodox monastery also contained a school for illuminating manuscripts.

Legends of treasure and spirits flow from this this fairy tale-like oasis.

German and American troops joined forces to defend this fortress during the strangest battle of World War II.

Remnants of the Nazis' occupation of Denmark linger along the sand.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.