The topiary maze at the Habsburg hunting lodge.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

What was once supposed to be the symbol of a shining Afghan future is now a bombed-out ruin.

Pilgrimage site for star-crossed lovers.

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

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Hear the quietest sound from across the dome.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Elaborate tile work in this railway station tells the story of Portugal.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

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

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

The somber sculptures commemorating Irish Famine on the river Liffey in Dublin.

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

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

Birthplace of the "Cat in the Cradle" and a cluster of iconic, original windmills that let the Dutch tame the seas.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

Unsurprisingly, Holland is home to one of the most magnificent flower gardens in the world.

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