Stockholm's deepest subway station is also a stunning ecological wonder.

The library's graceful rotunda is like a bibliophile's temple.

Dine on food tied to Viking history and legend at this subterranean Stockholm spot.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

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

What looks like a crashed Zeppelin is actually a bright, airy reading room perched atop a modern museum.

A bust of Franz Kafka spins in pieces, reflecting the writer's inner torment.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

This artificial cave looks like something out of a fairytale.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

A hidden subterranean installation offers a view of the sky.

San Franciscans leave gifts and messages for the magical beings that live behind the tiny, mysterious door installed on a tree in Golden Gate Park.

This chapel is the site of a yearly pilgrimage that originated during the Middle Ages.

A small Portuguese cottage formed between boulders in the countryside.

A stunning 18th-century site where pilgrims ascend by a series of punishing stairs only to return via funicular.

A small but charming botanical garden that contains many exotic plant species.

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

This restored Portuguese cafe may well be the most beautiful place in the world to grab a Big Mac.

The stunning interior of this Gothic church is covered in ornate gold details.

The crumbling ruins of an abandoned 12th-century monastery.

Blue-green pools and smooth stones comprise one of Spain’s most idyllic hidden wonders.

These rock drawings in the Côa Valley also create an ancient optical illusion.

One of the world’s longest pedestrian suspension bridges.

One of the few places in Portugal where the Celtic ritual of wearing large wooden masks is still practiced.