This 700-year-old structure is one of the most unique architectural and historic monuments in Gdańsk.

The site of the first battle of World War II.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

An underground city of salt.

One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

A temple to modernity, tucked away amid Barcelona's more well known museums.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

Week-long block party becomes a competition for the best decorated street.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Mountain where Jesus was first tempted by the Devil.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

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.

A beautiful but toxic fountain of mercury.

This semi-secret storybook hedge maze is also the oldest garden in the city.

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

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

A state-of-the-art medical facility from the Imperial era is now a derelict ruin.

The site of the famous Nazi book burning campaign of 1933 remembers its "Night of Shame".

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.