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

The verdant mossy ruins of a Franciscan monastery lie in the remote Sintra hills awaiting exploration.

These moss-covered medieval ruins tower atop the smallest of Ireland's Aran Islands.

This Bronze Age tomb is the centerpiece of a clearing within a beautiful Irish forest.

This 5,300-year-old tomb with mysterious carvings crowns an Irish mountain.

Impressive mining ruins overlook a spectacular view of Ireland's Copper Coast.

These imposing walls and towers look more like the ruins of a fortress than a monastery.

On the Irish coast, 18 members of the Howard family are eternally resting in an Egyptian pyramid.

Ruins battered by centuries of war and disaster offer a wondrous glimpse of medieval Ireland.

You can see three Irish counties from this Neolithic hillside fort, once the seat of the Kingdom of Ailech.

Achill's most recently abandoned village dates back to to the Age of Enlightenment.

The remains of this deep, dark mine have left behind a haunting rocky warren of tunnels.

A standing relief of a Norman knight whose posture marks him as a Crusader.

This ancient Irish tower could easily have stood in for Rapunzel's prison.

A moody and picturesque riverside ruin overgrown with vegetation.

The ruins of an 800-year-old monastery boasts the tallest round tower in Ireland.

After being destroyed by IRA sympathizers, the ruins of this stately Irish manor have sat vacant for decades.

This controversial Irish show cave is home to a massive formation known as the Great Stalactite.

The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

While only two of the ancient buildings at this site are actually churches this was one of the earliest Irish pilgrimage sites ever.

There might not be much left of these Irish ruins, but their linguistic legacy is still going strong.

This singular Irish dolmen is more Frank Lloyd Wright than upright stonehenge.

The enchanting archway is the only surviving portal into Dublin's lost medieval wall.

An Iron Age fort on the edge of a seaside cliff offers a glimpse into an ancient, mystical world.