These sprawling mines once served as a source of plaster and today serve as a storage facility.

This museum sits on the site of a decommissioned military communications base.

A remnant of the last Ice Age, this lake is surrounded by fascinating rock formations.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

Explore the wide world of desert plants at this unique Palm Springs botanical garden.

These massive concrete balls were used to mine gold in Virginia.

The quiet field that inspired one of the most famous songs of all time.

The “Thumb” of Mauritius provides a 360 degree view of the entire country.

This small group of sand dunes manages to pack in a strange rainbow of colors.

This terrifying glass bridge on the side of a mountain cracks as you step on it.

This colorful overpass is one of Bhutan's longest suspension bridges.

A factory director designed what was the world's longest suspension footbridge in 1923 so his employees could get to work safely.

A symbol of friendship between the mountainous regions of Switzerland and Bhutan.

This expansive bridge in the Canadian wilderness was originally just built for friends.

This series of rope-style bridges brings visitors into a jungle layer that is usually reserved for birds and monkeys.

At nearly 1,000 feet long, this astonishing glass suspension bridge is one of the longest in the world.

The latest in a series of long glass bridges suspended at terrifying heights.

This dizzying span over the ancient Algerian city was once the highest suspension bridge in the world.

A backdoor to Machu Picchu that only the most foolhardy infiltrator would attempt to breach.

Crossing this suspension bridge feels like walking through the sky, a fitting tribute to the head of the Apollo program.

These decaying bridges 1,000 feet high are a reminder of the skill it took to cross the Colorado Rockies by rail.

This Nigerian nature reserve is home to the longest canopy walkway in Africa.

A tiny red pebble marks what may be the quietest outdoor spot in the United States.

A precariously balanced rock perches on the edge of a cliff created tens of thousands of years ago by glacial erosion.