Longest fortress system anywhere in Europe.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A musical instrument played by the sea.

On a small Slovenian island, diners can mix and match a classic cake into dozens of sweet and savory flavor combinations.

A whimsical bridge adorned with decorative dragons.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

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

The modern birthplace of Irish freedom.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

Inscribed on the gate are the names of 29 figures from the University's first five centuries.

Displaced highlanders would take shelter from the wet Scottish climate under the large walled bridge at Glasgow Central Station.

Touching this 18th-century Scottish philosopher’s toe allegedly conjures good fortune.

This stately monument has been wearing a traffic cone hat for decades much to the delight of the locals.

A 200-year-old collection of oddities and medical paraphernalia.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

This ancient theater was once the home of fierce gladiatorial battles.

This salt marsh in Southern France is as pink as the flamingos that inhabit it.

Montmartre's sole surviving windmill became an iconic landmark for 19th-century painters, artists, and bohemians.

A 14th-century abbey founded by a forest-loving order of monks now sits in the center of a pristine nature preserve.

This Renaissance palace features a unique architectural design and is now home to the Ferrara National Art Gallery.

A portrayal of two lamps embraced and in love.

This deceiving white sand beach gets its brilliant hue from the chemical discharge of a nearby factory.

This beautiful 150-year-old synagogue survived Italy's fascist period and the Second World War.