This tiny island featuring 9th-century Viking ruins is only accessible at low tide.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

This tidal island, a sacred site in early English Christianity, was the target of a notable Viking invasion.

Deep in a Polish forest, this collection of Iron Age megaliths still holds onto many of its ancient secrets.

These unknown Bronze Age earthworks are believed to be ancient burial mounds.

It's possible to walk inside one of the largest Neolithic tombs in Britain.

This ancient stone necropolis is in danger of disappearing.

A Neolithic tomb hidden among a spectacular boulder-strewn stretch of coast.

A mysterious Neolithic tomb is perched along the edge of a modern golf course.

The largest portal tomb in Europe has a capstone weighing around 150 tons.

One of Europe's largest groups of dolmens remains largely off the typical tourist track.

A 2,000-year-old Iron Age fort offers stunning ocean views.

The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

Initially meant to immortalize the valor of the colonizer, this monument is now a symbol of Mauritanian resistance.

A Victorian Gothic masterpiece housing a world-class collection of rare books and manuscripts.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

On a secluded beach is one of the few shipwrecks left on the shores of Mauritania.

One of Alaska's most significant ancient sites, spanning millennia and cultures, is right under the feet of some famously fat bears.

A museum built around the site where the most controversial human remains in the country were found.

The largest salt farm in the Canary Islands is located at the foot of an active volcano.

One of the oldest structures in Helsinki is this burrow grave that dates back to the Bronze Age.

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

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