The largest Roman amphitheater in the Balkans once held over 20,000 people, but managed to lay hidden for hundreds of years.

This ancient theater was once the home of fierce gladiatorial battles.

An ancient Roman theatre restored to its former glory in the Spanish city of Cartegena.

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

This ruined fortress was the stronghold for a persecuted medieval leader and his infamous Assassins.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

An unlikely neo-Gothic castle in the Paraguayan countryside.

The legendary cliffside castle of three-time Voivode of Wallachia, Vlad the Impaler.

Abandoned castle was once a grand example of Russian privilege, built exclusively to win a frivolous bet between noblemen.

The gutted remains of this Estonian mansion are a monument to a tragic love.

Many famous English poets including Elizabeth Barrett Browning are laid to rest at this Swiss-owned cemetery in Florence.

A 14th-century abbey founded by a forest-loving order of monks now sits in the center of a pristine nature preserve.

A reservation-only highland forest reserve of endangered Pinsapar firs stands above a village in Andalucía.

In this African village, the walls of the chief's compound are painted with beautiful traditional designs.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

An underground mansion with fruit-bearing trees and grapes growing beneath the surface of central California.

Inside this magnificent 12th-century church is one of the finest carved wagon-roofs in all of England.

This mosque turned crypt is an amazing display of Persian-Islamic architecture.

This magnificent 18th-century hall consists of a maze of nearly a thousand interconnected passages.

One of the greatest maze designer’s greatest mazes.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

A Turkish monastery tucked into a cliff wall.