Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

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

The eerie remnants of an ancient forest were hidden under the sand for centuries.

Treehouse motel and treehouse-building school.

Islanders once used this dramatic, otherworldly landscape to hide their cattle from Viking raiders.

A massive underwater sinkhole made famous by Jacques Cousteau.

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

This cemetery features modernist statues as strange as its name.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

A swing to dangle you off the very edge.

Now famous as the "Harry Potter bridge," this impressive concrete viaduct has long been an icon in its own right.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

A fiery crater has been burning in the Karakum Desert since 1971.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

A Jenga-style cylindrical tower of books that appears to go on forever.

The real life Hobbiton, this sheep farm has been forever transformed since being built for The Hobbit film series.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

An Australian lake whose pink hue defies scientific explanation.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.