A series of modernist treehouse hotel rooms grace the outskirts of an Arctic forest.

Sweden's first nuclear reactor, R1, can be visited 25 meters underground.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

These 5,000-year-old cave paintings provide a glimpse into prehistoric Finnish life.

These lakeside pictographs were some of the first pieces of prehistoric artwork found in Finland.

This once-mighty brick factory is now a unique museum experience.

The tallest lighthouse in the Nordic countries was also the site of a bloody World War II battle.

The last permanent exhibit dedicated to the Soviet leader.

Finland's northernmost zoo is home to the country's only polar bears.

Nuclear waste experts study this prehistoric crater lake to envision landscapes one million years in the future.

Fortifications built for a Soviet invasion that never came now sit abandoned in a losing battle against nature.

A modest stone circle in North Wales.

After years of slow decline, a derelict Gothic castle is now being restored to life.

The enormous earthwork sculpture honors the ponies that lived and worked in the old colliery.

This Welsh village gave itself a ridiculous name in a publicity stunt a century ahead of its time.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

The ruins of this monumental city founded by the first Roman Emperor are strangely overlooked by most travelers.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

This legendary city has been a tourist attraction for centuries.

This massive chalk hill carving is one of England's most beloved giant horse geoglyphs.

The bronze uniforms commemorate the vital role of women during World War II.

There are hundreds of secret WWII bases hidden in British forests. Built to fight a Nazi invasion, they remained unknown for decades.

The London statue that imitates passersby.

A vortex fountain that seems to rise out of the ground.