This triumphal 16th-century arched gateway leads to the oldest street in Palermo.

In downtown Oslo, a menacing and terrifying relief clings to a church wall.

A museum celebrating the Canadian forces that liberated Belgium from the Nazis replete with battlefield miniatures and multiple Gardens.

This former Masonic lodge has been transformed into part museum, part bar, all awesome.

Christ's blood preserved in a Belgian town.

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

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

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

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.

The world's oldest bookshop still in operation.

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

The nearly 200-year-old folly has a secret spiral staircase hidden in one of its pillars.

This gorgeous space is England's largest independent library outside of London.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

The medieval woodcut-style artwork chronicles life in medieval London.

This bewitching Babylonian goddess haunts a hallway of the British Museum.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

These mysterious Viking chess pieces spent centuries hidden on a remote Scottish island.

A monument to the thrice mayor of London who according to lore made his fortune by selling his rat-chasing cat.

A statue of the legendary Celtic warrior queen who fought the Roman invaders stands in one of the cities she once destroyed.

The fierce beast perches atop a pedestal marking where the historic City of London gates once stood.

The cedar tree in Highgate Cemetery earned its title by accident.