The true depths of these stunning Moroccan caves are unknown.

This black shoreline is made up of exploded lava particles.

This once-popular otherworldly landscape was formed by one of the largest volcanic eruptions in history.

A serene temple with stunning stained glass hides in downtown Dallas.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

I-95's Tijuana-style celebration of kitsch at the Carolina border.

Floating swimming pool within a moored vessel.

Two stone columns flank the grand Venice square, but there were supposed to be three.

The walls and streets of the ancient city are peppered with penises.

Ancient snack bar of the Roman Empire re-opened.

Erotic art covers the walls of the largest ancient pleasure palace.

Go inside to really appreciate this 500-year-old technological masterpiece.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The glowing blue Nymphaeum of Emperor Tiberius.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

This curious, round temple is the oldest still-standing marble building in Rome.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

Inside this McDonald's you can dine on your Big Mac and fries next to a 2,500-year-old Roman wall.

Ancient ruins hidden underneath a modern luxury hotel.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.