Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

A church of bones, decorated with 40,000 human skeletons.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

The underground sanctuary of a mysterious ancient cult.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The celebrity luchadores of La Paz are tough ladies in traditional petticoats and braids.

The Arctic Circle runs through this isolated spot north of Iceland.

More than 300,000 historical artifacts from the famous music venue, from Duke Ellington's handwritten score to The Beatles' booking slip.

Lima’s Museum of Anthropology is lined with thousands of elongated human craniums.

An acoustic anomaly with a mysterious cause.

Colorful concentric circles honor a small Croatian town's supposed spot at the nucleus of it all.

This military tunnel dates back to World War II and provides visitors with a little wartime adrenaline.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

When a supermarket opened up shop within a medieval building it became protected by UNESCO on a technicality.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

Longest fortress system anywhere in Europe.

This picturesque medieval monastery guards a small trove of historic treasures.

An ethereal glowing blue ocean cave in Croatia.