The ruins of this monumental city founded by the first Roman Emperor are strangely overlooked by most travelers.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

A seaside castle complex that stood through centuries of conquests.

The ruins of an abandoned medieval city where the last Byzantine emperor was crowned.

This legendary city has been a tourist attraction for centuries.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

The oldest stone house in Paris was built by its most famous alchemist.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

This massive library holds what was once the largest book collection in the world.

This bridge was constructed from the rubble of the infamous Bastille.

Notorious artist squat renovated into legal studios.

A sulfuric martian landscape that looks far better than it smells.

This tumultuous Icelandic lava field looks so alien European researchers want to use it as a stand-in for Mars.

Three columns of volcanic rock shoot out of the ocean.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

The most powerful waterfall in all of Europe.

This elegant arc of a waterfall marks a religious turning point.

Climb right into the heart of this colorful Iceland volcano.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Medicinal spa created with the discharge from a geothermal energy plant.