A six-story treehouse offers spectacular views of New York's Finger Lakes region.

This abandoned secret city is a crumbling wonderland of Soviet ruins.

A trio of giant wooden megaphones turn up nature's volume in this Estonian forest.

Man-made mineral caves house massive bat colony.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

Climb around the high waterfalls on series of iron ladders and bridges within the wildest gorge in the Slovak Paradise.

One of Chile's most active volcanoes is riddled with beautiful caves.

The largest radio telescope in the world searches for extraterrestrial life from the remote limestone peaks of southern China.

It took an artist 20 years to create this sprawling sculpture garden honoring the area's ancient inhabitants.

A unique zoological park home to over 30 species of wild cats, both big and small.

A surprisingly beautiful abandoned World War II military base in East Greenland.

A wooden street sign is the last remnant of this 400-year-old alleyway.

Thousand-year-old trees tower within one of the world's only inland temperate rainforests.

A curiosity-seeker's paradise set inside a three-story historic school house.

Explore a uniquely pristine Borneo forest, now protected by former headhunters turned tour guides.

Ferdinand Magellan dubbed the world's largest water village the "Venice of the East."

One of the largest caverns in the world has a maw large enough to stack cathedrals in.

These jagged limestone blades cut out through the canopy of the jungles of Borneo.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

The names Lúthien and Beren can be found inscribed on the shared grave of the famous writer and his beloved wife and muse.

You'll need cowboy boots to trek to this old-fashioned saloon nestled in a giant natural cave.

This mountain sunrise is one of the most breathtaking views in Thailand, yet well off the tourist trail.