This 18th-century fort surrounded by a moat was used to store gun powder and ammunition, and now sits in the middle of a large part in Dublin.

The gnarled remains of an exploded German bunker from World War II sit along a breathtaking fjord.

Journey through the ruins of this ancient Roman temple dedicated to the god of war.

This North African stone complex is considered to be the oldest astronomical observatory on Earth.

This observation tower is one of two of its kind that still exist in the United Kingdom.

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 last remnants of a massive medieval wall that once encompassed the city of Berlin.

From grand battles to daily life, this Spanish museum offers a view of world history in miniature.

A medieval stronghold rising over the ruins of ancient Roman villas along Rome's southern coast.

This reconstructed Norman castle is the world's most accurate, from location to livestock.

This medieval tower is all that remains of the castle where Joan of Arc was held before being burned at the stake.

The ruins of a 13th-century monastery that long served as a place of refuge from wars and raids.

A magnificent, long-abandoned castle built in the wake of the reconquest of Spain.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

According to the Soldiers Account Book, the village of Odiham is home to Thomas Atkins, whose name became shorthand for all British soldiers.

A submerged archeological park still holds the wonders of a Roman Sodom.

Virgil's many-mouthed gateway to the underworld.

A tree that defies gravity grows in an ancient ruin.

A defensive structure built during the Hundred Years War has remained useful in one way or another for nearly 700 years.

The original movie set for the home of 'Star Wars' hero Luke Skywalker.

An abandoned film set location for a remote spaceport in a galaxy far, far away hides in the Tunisian desert.

A seemingly simple canyon that was the backdrop to a number of famous movies.

The Roman Emperor's lost summer home and grotto full of enormous sculptures sit along the Italian seashore.

Located more than 600 feet beneath sea level, this tunnel boasts the world's first undersea roundabout.