The site of Paul Revere's historic two lantern warning.

A centuries-old church stands as a testament to Boston's "father of architecture."

The oldest Italian café in Boston, this spot also serves as a veritable museum of vintage coffee ephemera.

Millions of numbers carved in glass represent the tattoos forced upon victims.

Once a resting spot for King Fernando VII.

The train platform where Jews were sent to concentration camps is now preserved as a Holocaust memorial.

An exclusive waiting room built for the royal family in the 1920s is hidden in Milan’s central station.

This grisly effigy displays an early Christian martyr who was skinned alive and beheaded.

The mark of the Devil's horns on a marble column in Milan.

Just across from the "Last Supper" painting is the famous painter's vineyard, a gift received for creating the masterpiece.

A brutalist gem towering over the heart of Milan.

See what remains of a once grand ancient Roman circus.

The secret medieval communication system will whisk your words above the noise of the crowd.

This giant middle finger statue sends an unambiguous message to Italy's bankers.

Nestled in the heart of Milan is a real wunderkammer of morbid curiosities.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

"The prettiest love letters in the world" ... or so said Lord Byron.

Small on the outside, big on the inside, this church is an astonishing act of visual deception.

Two very green residential towers cleaning the air in one of Europe's most polluted cities.

This influential Renaissance-era library was once the haunt of kings and monks.

Originally used to sell brandy, the bull-shaped billboard became an iconic symbol of Spain.

A rare set of strings by famed instrument maker Antonio Stradivarius is on display in the Royal Palace.

This historic fountain is a favorite neighborhood meeting point.

Stockholm's deepest subway station is also a stunning ecological wonder.