The plunge pool is a surviving relic of a rowdy royal residence.

This 8th-century Bavarian monastery is home to an exquisite Baroque-era library.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

The hidden ruins of an old hydroelectric plant reclaimed by nature.

A 2,000-year-old engineering wonder hides beneath an Italian town.

The alleged birthplace of Lady Jane Grey, who was executed at age 16 for claiming the throne of England.

This recently restored crypt was once plagued by liquefying coffins and exploding caskets.

Historical figures from New York City's Catholic community reside in Midtown.

It was meant to help transport wounded soldiers to a secret underground hospital.

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

These ruins of a medieval church are full of architectural mysteries.

The ruins of a medieval castle that once belonged to one of the most powerful families in the Netherlands.

The ruins of this medieval tower are destined to crumble into the sea.

A hidden plaque is the only reminder of the lost palace where two storied English kings were born.

The largest and best-preserved Roman amphitheater in Africa was designed to seat 35,000 people.

One of the most poignant ruins of the Chernobyl nuclear disaster, the local football team's stadium has been quickly reclaimed by nature.

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

The main gates have been locked since 1745 and will remain so until the Stuart Dynasty returns to the throne.

This museum sits on the site of a decommissioned military communications base.

It’s said this crypt was the setting for the tragic finale of the Shakespeare play.

This grisly exhibit houses skeletons and weapons from a devastating 14th-century clash.

A once crucial portion of the Long Island railroad still lays abandoned, waiting to be turned into an urban park.

Only a fragment of this 15th-century Dance of Death survives today.

Obscured within a ring of trees, this abandoned World War II relic hides on a German hillside.