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

Major tourist destination known for its bubbling mud-pools and hot thermal springs.

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

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

A marvel of Byzantine engineering under the streets of Istanbul.

Catacombs turned marketplace.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

A battle between nature and architecture in the Cambodian jungle.

Come for the flowers, stay for the bats!

A six-ton wedding present for the King of the Scots.

Climb inside an iron crystal magnified 165 billion times its normal size.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

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

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

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

A little sculpture with a large wardrobe.

A walk through the historic city center, under the streets of Seattle.

World's first "penitentiary," meant to be humane, drove men insane.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

Famously misunderstood wonder of the ancient world

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

The celebrated eyesore created by starry-eyed sweethearts.

Eighty million natural history specimens call this gargantuan museum home.