Solar observatory doubles as a daring display of Expressionist architecture, much to Einstein's chagrin.

A six-story, asymmetrical tower filled to the brim with scientific experiments.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

Metro station with a claim to rock n' roll fame.

An impressive collection of massive radio satellites.

A massive explosion that leveled hundreds of buildings in the city of Leiden is remembered by a waterside plaque.

This historic Dutch newspaper building is covered with media-themed details—and one unrelated oddity.

This 17th-century "unicorn" was cobbled together from the skull of a rhinoceros, the legs of a mammoth, and the horn of a narwhal.

An unassuming rod in the Netherlands was once the old standard unit of length for the entire Dutch empire.

What many consider the original prime meridian and westernmost point of the old world.

Iron Age grave stones and Viking burials, a short drive from Gothenburg.

Controversy surrounded the creation of this anti-fascist statue.

Dedicated to a song so popular the request to "Play Shoreline" became part of Swedish culture.

A 200-year-old collection of medical paraphernalia in a historic house.

The charming storybook building now houses a small police museum.

One of the world's few mounted blue whales, its jaws are hinged open allowing visitors to descend into a lounge.

A Gothic-inspired fish market is Gothenburg's best place to find loaves and fishes.

There are no crying babies in this neck of the woods.

A statue of the Swiss cartoon character stands outside the school that inspired his creator.

A rare, flower-shaped example of Brutalist architecture in Switzerland.

This secret Swiss fortress is disguised as a harmless pink house, complete with fake windows.

This long line of cement defensive wedges is named after the famous chocolate bar for obvious reasons.

Over 3km of caverns and caves at the Switzerland-France border contain the largest underground river in Central Europe.