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

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

The only known mosaic depicting the Greek god of sleep, Hypnos.

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

The majority of the highest mountain in Poland is actually located in a different country.

The 700-year-old fortress was the site of Count Orlok's castle in "Nosferatu."

The world's newest astronomical clock is also its most accurate.

Two gravestones clasp hands over the religious divide.

A beautiful maze marks where three countries meet.

The tallest mountain in mainland Netherlands isn't actually very tall.

Visit the ancient, mysterious Roman catacombs ... in the Netherlands.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Incredible labyrinth of man made caves.

This historical Netherlands fortress still bears the marks of its single siege.

This centuries-old gothic monster has been converted into a sprawling, glossy bookstore.

At this barrel organ museum, history and live concert keep Dutch street organ culture alive.

The Bloemen Route, or “Flower Route”, stretches 25 miles through prime Dutch tulip country as a result of “tulip mania,” the world’s first economic bubble.

The heart of Dutch football history.

This towering church is home to a world-famous organ and a treasure trove of medieval art.

Oldest Museum of the Netherlands is a true cabinet of curiosities.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

This giant wire frame man sculpture is crouched in contemplation.

The world's largest collection of ships in bottles.

This miniature take on the Kremlin is one Dutch man's retirement project.