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

The Polish capital has had a deep connection to its guardian mermaid for almost a millennium now.

There has been an astronomical clock on this spot since the 14th century.

Explore this medieval cathedral by trying to spot all the malevolent monsters hiding in its beautifully colored windows.

The telescope that discovered Neptune.

World's largest bell sits on the grounds of the Kremlin in Moscow.

The longest and tallest aqueduct in Britain can actually be sailed across.

A rare wooden coffin set vertically into the Gothic arch of an ruined church.

Mysteriously stacked storefront paths give this medieval British town an iconic style like none other.

The western face was supposedly left clock-less to snub the Welsh.

A mysterious demonic figure peers down from its perch within the gorgeous Chester Cathedral.

This aging storage facility is the world's largest brick warehouse.

Charles Dickens described the concert room in this amazing Victorian hall as "the most perfect room in the world."

This bronze statue was dedicated to a 1966 Beatles hit.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

The oldest surviving wooden bridge over Rhine lets travelers cross easily from Switzerland to Liechtensten.

This museum tells the story of lake dwellers from 4000 BC to 850 BC, replete with stilt houses and goats.

Visitors dating back to the 1600s carved their marks in the stones of the iconic tower.

A Swiss amusement park entirely dedicated to the theory of ancient astronauts.

If James Bond bungee-jumped off the side of a 720-foot dam, would you do it too?

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Originally planted by the ancient Carthaginians, this sprawling palm grove is one of the largest in the world.

Bacteria and algae give the salty water its bubblegum hue.

A small but immensely extravagant palace built by the "Night King."