A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

This stunning, out-of-the-way Croatian monument commemorates a community's uprising against occupying fascist forces.

Yugoslavia's biggest underground airport lies in ruins.

An ethereal glowing blue ocean cave in Croatia.

Villas that once served as playgrounds for the rich now fall away in decay.

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

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

This honeycomb-textured tafone looks like a petrified troll head.

Pigduck of Turku.

This intricately spiralling forest was created as a monumental work of art.

These Finnish rapids have been attracting tourists for over a hundred years and are now released with the push of a button.

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

This disused church, left to the elements of the Arctic Circle's forests is open for exploration.

If you visit Santa's village, you can get your passport stamped to show you crossed into the Arctic Circle.

The smallest restaurant in the world.

Hidden deep in a forest is this geological wonder carved by glaciers.

Roughly 17 million letters to Santa have found their way to this Arctic Circle post office.

A small island dotted with old, historic Finnish buildings.

A beautiful Arctic museum and nature center preserves the culture of the Sámi people.

A little-known sculpture park of contemporary environmental art in a Lapland forest.

Crawling into this primordial cave may feel disconcertingly familiar.

In the Hugging Tree Forest, lingonberry marshmallows, hot chocolates, and the best campfire lattes north of the Arctic Circle come to you.

This irregularly shaped sea fortress has defended not one but three different sovereign states.