This ducal residence was once home to a future Russian empress and a French king in exile.

Flamboyant architecture from the turn of 20th century.

3,000 market stands in five former Zeppelin hangars.

A former Latvian headquarters of the brutal KGB secret police is now open as a grim reminder of their atrocities.

A miniature train-ride through Slovenia's largest cave system.

This massive subterranean fissure is known as the "underground Grand Canyon."

This one-time health resort was used by aristocrats around the world.

This cafe offers a curated collection of treats and tipples made by monks and nuns.

One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Mysterious 500-year-old tapestries depict a unicorn hunt.

This museum is housed in an unassuming building that witnessed one of the most daring feats of satire in modern history.

Housing the groundbreaking maps and globes of Gerard Mercator.

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

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

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

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

Hiding the longest subterranean river known in the world.

This noble mash-up in eastern Luxembourg is part Medieval, part Renaissance, all castle.

Dynastic Home of the De Piro Family.

A centuries-old forgotten underworld lies beneath Malta.

The floor of this spectacular Baroque sanctuary is covered in memento mori.

Norway has built what may be the world's most beautiful public toilet.

This small condiment museum makes all manner of mustards with a 200-year-old mill.