A scientific observatory managed the largest Portuguese astronomy research unit.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

A memorial in the Tiergarten is a reminder of the suffering inflicted on homosexuals by the Nazi regime.

Where Mary Shelley’s "Frankenstein" and John William Polidori's "The Vampyre" were born.

This stone in Lake Geneva was once the reference point used to determine altitude in Switzerland.

A treasure trove of scientific instruments from the 17th and 18th centuries.

Switzerland's oldest public observatory is an important part of the Zurich cityscape.

Hidden in the garden of physicist Erwin Schrödinger's house is a life-size figure of a cat from his famous thought experiment.

A 200-year-old tavern challenges guests to finish a glass of wine while hanging from a ceiling beam.

This massive boulder was hurled into a Zurich church when a gunpowder depot was struck by lightning in 1652.

The oldest skyscraper of Europe now stands dwarfed by the surrounding structures.

An ancient Egyptian temple sits within a modern European museum.

The remains of a medieval wall discovered in the basement of a jewelry store.

The location of the world's first telescope demonstration.

A giant yellow phallus sculpture hidden in the gardens of the Museum Boijmans Van Beuningen.

An art installation memorializing a tram stop, which became a tram stop.

The site of the original experiment that would be used to disprove the theory of luminiferous ether.

There are hidden patterns on the subway seats of some Stockholm metro cars.

Krakow's own version of the Hollywood Walk of Fame.

Remnants from a time before electricity.

The last remnants of a massive medieval wall that once encompassed the city of Berlin.

At one of Berlin’s oldest churches, visitors can place mosaic tiles to help restore a medieval mural.

Where visitors can play more than 150 retro arcade games.

A Soviet era flat that refused to conform to the dull gray standards.