The final resting place of soldiers' loyal canine companions.

A six-ton wedding present for the King of the Scots.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

360° views of the city plus five floors of optical illusions and hands-on science.

Touching this 18th-century Scottish philosopher’s toe allegedly conjures good fortune.

The ruins of this gorgeous clifftop castle look like something from a fantasy novel.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

The world's largest wooden structure.

Rare karst landscape eroded from a flat seabed.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

A Spanish town built into the cliffs.

One of the most spectacular bridges in Spain spans a narrow chasm that divides the city of Ronda.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

These mysterious ancient stone spheres were created by a civilization lost to time and are now mostly lawn ornaments.

This neon blue river gets its color from a unique mix of bacteria and volcano minerals.

A secret climbing tree hides along the side of a Costa Rican road.

Sofia's legislative center is continuously reinventing itself.

An homage to the medieval rulers of Bulgaria.

A vast Communist-era exhibition space in the Bulgarian capital.

"Holy Wisdom" overlooks the city that became its namesake.

A gigantic statue of a Russian soldier watches over the ancient city of Plovdiv, a prominent reminder of the Soviet period in Bulgaria.

A magnificent, glittering building tucked into a tiny Bulgarian mountain town.

The remarkably well-preserved final resting place of a powerful ancient Thracian king.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.