Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

A silly medieval mural preserved on the side of a Viennese house.

A Trabant car, a kangaroo statue, and a plethora of plants take over this abandoned-factory-turned-bar.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

This sculpture honors the man who was known as the "Righteous Among the Nations."

Sprawled across the Great Hall ceiling are various constellations and images relating to the zodiac.

Tiny effigies of the victims of Edinburgh's famous Anatomy Murders.

A succession of eerily contemplative iron figures lead from a Scottish museum to the sea.

One man spent 10 years building a spectacular section of road because no one else would.

A library where thousands of books explain how to avoid another Great Recession.

Come for the oysters, stay for the priceless art honoring inventors across history and Scotland's favorite outdoor sports.

One of Scotland's most important modern structures, it just made the '100 Most Endangered Sites' list.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

An American ghost town hides along a side street in Scotland's capital.

Largest lake in Great Britain measured by surface area.

A scattered trail of street art adds a pop of color to the city's stark structures.

Climb this overlooked gem's spiral staircase and you'll be rewarded with spectacular views of Glasgow.

A local tree surgeon has created a whimsical walk full of carved tree stumps near Scotland's Loch Lomond.

The secret medieval communication system will whisk your words above the noise of the crowd.

A bus with a butt and biceps to put Olympic athletes to shame.

A massive, abstract lookout tower providing a panoramic view of Prague.

Dedicated to the unsung history of human waste.

A plaque marks the spot where the saint was shoved off the Charles Bridge and into the river.