Stockholm's narrowest alley is barely over two feet wide.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

The world's largest model of our planetary system.

The library's graceful rotunda is like a bibliophile's temple.

This inverted metropolis model is the artist's "revenge" for not being allowed to have a doll house as a kid.

This unique architectural wonder is home to luxury apartments.

Once a meeting point for great thinkers, and the midpoint of the country.

A public display of random paleontology.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

Mounds, rune stones, and a 1,000-year-old church, left behind by Denmark's first two kings.

Denmark’s never-ending bridge.

The original home of the Lego has a huge amusement park dedicated to the iconic plastic toy.

An enormous playhouse designed to look like 21 stacked Lego bricks, with another 25 million colorful Legos inside.

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

Climb to the top of its spiral spire for spectacular views of Copenhagen.

A little-known cafe in an old copper bridge tower with 360-degree views of the harbor.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

The world's first clock to use set theory as a measure of time required the invention of a new light bulb just to maintain its obtuse measurements.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

This monumental work of art symbolizes the coming together of a previously divided city.

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

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

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

A monument to the three wars that led to German unification towers within a Berlin traffic circle.