This snug medieval lane is one of the narrowest streets in the world.

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

The hallucinogenic center of the ancient world.

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

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

Home to three historic ships from the age of Vikings.

This functioning parish church is also the site of many concert performances due to its wonderful acoustics.

Hamburg's first legal sex work is relegated to a gated street that still does not allow pedestrian women.

Hamburgers are intensely proud of their tunnel beneath the river.

Once the tallest building in the world, this abandoned church is now a monument to the destruction of WWII.

Cold war icon and onetime "hole" in the iron curtain.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

One of Ireland's most infamous prisons for rebels including men, women and children.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

The modern birthplace of Irish freedom.

If you can look past the nearby sewer pipes, this urban sinkhole grotto is a mini-paradise.

These azure waters were thought to lead to the Mayan Underworld.

Years of archaeology, just chillin' by the water cooler.

Elevated freight railway turned wildly successful urban park.

This abandoned subway station can still be seen on regular commuter trips.

The notorious headquarters of a corrupt political machine.

Nope, not Washington Irving's house.

Great place to have a drink and a bite to eat in an atmosphere laden with New York's Bohemian past.

Named the fifth most beautiful building in America in 1885, this former courthouse boasts the best view in the Village.