A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

The longest navigable underground river in the United States is home to countless blind and albino animals.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

A mysterious castle built as a monument to lost love.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

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

Collapsing castle on the Hudson river was once the storage site of military surplus business.

A clear blue swimming hole with hidden caves, still unexplored.

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Experience park where visitors are told to expect the unexpected.

Northern Ireland's Brobdingnagian stepping stones.

This futuristically sylvan church is a glass-enclosed marvel of modern architecture.

An unusual round church in London with a Templar past.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

Quite simply the largest tree in the world (by volume).

Every autumn, this hillside is ablaze with red summer cypress.

Eighty million natural history specimens call this gargantuan museum home.

An Australian lake whose pink hue defies scientific explanation.

No one knows how this Pacific Northwest spruce tree came to have so many trunks.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."