Explore the dark underground corridors of this graffiti-covered former military fortification.

This World's Fair showpiece was built in Chicago, but shipped to Maine.

The widest waterfall in Europe is a natural wonder and one of the only places where fish are caught in the air.

Beautiful natural falls where Satan once ruined a pot of beans.

A limestone wonderland of water and subterranean secrets.

This neon blue river gets its color from a unique mix of bacteria and volcano minerals.

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

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

This large midwestern cavern features impressive rock formations and an underground waterfall.

At the center of an island in the middle of the Indian Ocean is a deep chasm ringed by tall waterfalls.

Nature's water park in the Wadi Bani Awf valley is full of pools flanked with cliffs and natural water slides.

Two massive rock outcroppings on the Oregon coastline.

This beautifully designed star-shaped fort was the premier defense system of the late 1500s.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

Take a schvitz just like an infamous Soviet dictator while his unblinking eye looks on.

According to legend, this boat-shaped henge is built over the grave of a mythic king.

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

The world's first ice hotel is still one of the most elaborate and beautiful.

This frequently-photographed waterfall takes only a short hike to visit.

A French chateau, failed utopian community, odd museum, and Stonehenge replica in rural Washington State.

The longest continuous lava tube in Oregon.

Bridges, terraces, and replicas of historic structures all built of rock and petrified wood by one man.

A volcanic fissure over two miles long and up to 70 feet deep.