Forts

The castle still holds traces of the abandoned Roman fort it was built atop.

Ireland's most remarkable collection of these curious cone-shaped houses is worth the buzz.

This striking fort on the Maginot Line looks just as it did after being destroyed in the Fall of France.

A full-scale replica of a 1774 colonial settlement in Kentucky.

Historians and hobbyists head to this former French outpost for the annual Feast of the Hunters' Moon.

This now-deactivated naval base defended the Florida coast for centuries.

Once a lonely sentinel on the edge of the Great Plains, this rebuilt trading fort offers a glimpse of life on the Santa Fe Trail.

This four-story steel sphere in Maryland was used to test biological weapons.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

This Puget Sound military post has a long, turbulent history as a gateway to the Pacific.

A World War II gun battery sits at the easternmost point of North America.

The mile-long pier stretches from a ruined fortress out into the Baltic.

An abandoned network of military bunkers and tunnels open for anyone willing to descend into the darkness.

A stone circle on the slopes of a Caribbean volcano commemorates the leader of an anti-slavery uprising.

A half-mile-long stretch of medieval forts built after a devastating pirate attack persists amid the modern port city.

A hidden art gallery in an abandoned Warsaw fort.

Abandoned blockhouses from Nazi Germany's Atlantic Wall erode into the sea on a French beach.

This strategically placed hill fort has served defensive forces from the Iron Age up until the 20th century.