Fortresses

These beautiful historic watchtowers were used for both scanning the desert for enemy invaders and observing the celestial world.

An abandoned Byzantine fortress and notorious prison.

This huge abandoned fortress hidden inside a mountain holds a world of subterranean secrets.

The largest and, arguably, most scenic fortress in Bhutan.

The remains of a magnificent medieval fortress that was the capital of a vast empire.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

Every spring, locals see the shadowy figures of a ghost army of slain Greek soldiers descend upon this ruined fort.

Legend has it a commoner volunteered to be buried alive in the foundation so that the great fortress could be built.

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

Croatia's "hairy stone" fortress is one of the most well preserved Istrian castles.

The Renaissance-era courthouse is a relic from the fortified town's centuries of Venetian rule.

An archaeological treasure trove towers over the valley of Chiavenna.

The medieval town's star-shaped walls are geometrically dazzling, though not entirely impenetrable.

Hidden dwellings in the cliffsides of North Togo used by local Moba tribes to evade 18th-century slave traders.

This almost-forgotten underground dungeon housed several convicts over the years, including Caravaggio.

An 11th-century mountaintop fortress that played a crucial role in Italy's papal wars is now a vacation rental.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

This 15th-century island fortress later served as home to the executioners no one wanted to live near.