The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

A World War II evacuation tunnel turned into a history display of Croatian state and people.

This 135-year-old weather station studied the effects of the climate on human health.

An eclectic art form practiced by untrained masters is celebrated at this museum in the heart of Zagreb's old Upper Town.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

Where the lovelorn find a home for their sentimental keepsakes.

This chimerical bridge/tunnel appears to dead end right into the sea.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

Terrifically morbid cemetary and site of famous Paracelsus' grave.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

You can spot this teeny tiny stained-glass window from the Bonifacius bridge.

The compass on its front was a handy tool for 17th-century merchants who needed to know the direction of the wind.

This gruesome biblical parade celebrates the one day a year that a bit of Jesus' blood turns to liquid.

Christ's blood preserved in a Belgian town.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

This equestrian statue of Constantine the Great has been the subject of criticism for centuries.

Breathtaking and huge 430 year old maps of Italy.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

An ancient Roman temple first dedicated to an emperor's wife is now a church.

A rather vulgar example of the transition from Latin to the Italian vernacular.

This ancient Roman arch misled treasure hunters for centuries.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.