Walk 2,300 feet above the ground on the "Troll's Tongue."

This isolated island is often capped by its own fluffy cloud.

Located more than 600 feet beneath the North Atlantic seabed, this tunnel boasts the world's first undersea roundabout.

Thousands of miniature bronze sculptures have taken over this city square creating a unique art installation.

A Nazi concentration camp and Anne Frank's place of death.

Hamburgers are intensely proud of their tunnel beneath the river.

A tiny island is connected to the mainland by a private railway that residents travel in their own personal wagons.

At this bohemian accommodation, guests who dream of joining the circus can spend the night in themed wagons.

The shiny silver little brother to Copenhagen's Little Mermaid statue.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

The world's first combination ski slope and power plant.

Nordic giants resurrected from the sea and restored to their former greatness.

A spiralling hourglass-shaped tower rises from the forests in Denmark.

Perhaps the most spectacular grotto along the Algarve coastline.

A naturally occurring tunnel in this Nordic mountain makes it look like it's been shot.

The grounds and buildings of an old wood pulp mill have been transformed into an innovative art park and museum.

A stunning architectural yet functional feat, towering over Oslo.

A quaint medieval millhouse hovers surprisingly above the waters of the Seine.

Experience architect Le Corbusier's modernist design for living in the home he designed for himself.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

This massive library holds what was once the largest book collection in the world.

The narrowest street in Paris.

This museum explores the history of stickers and is home to RePEELed, an exhibit featuring sticker art from around the world.

This postmodern apartment block was designed to be a vertical neighborhood.