Monasteries on rock pillars, once accessible only by frayed ropes.

A castle perched precariously over the Crimean Sea.

The oldest museum in Russia is home to a fascinating collection of nearly two million anthropological artifacts and anatomical curiosities.

A tiny church on a man-made island in the Adriatic.

Structure built from the skulls of vanquished foes.

The bizarre rocks of Đavolja Varoš are the result of natural erosion.

A Roman monument to their own civil engineering prowess.

Imperial palace of Emperor Galerius, the Emperor behind the worst Christian persecutions during the Roman Empire.

A giant portrait of an ancient king looms over the river.

Sealing couples' love since just after World War I.

Stone age urban planning.

Celebrated example of Ottoman architecture that also served as a site for brutal massacres.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.