A breathtaking 19th-century trail overlooks Lake Tahoe.

This trail follows unique stone railroad tracks and a historic waterway to the south coast of Devon.

This harsh mountain path was built as a strange attempt to improve the health of Turkmen citizens.

The longest non-mortared wall in the country is one man's tribute to his displaced Yuchi ancestor's five-year journey to her homeland.

A dictator's failed public works project has been reborn as two linked trails through spectacular scenery.

A trail weaves through the verses of a poem illustrated by stone sculptures inspired by Native American pictographs.

A series of 33 stone markers maps an ancient 55-mile transportation route.

The beehive-like buildings of this abandoned resort reside near the border of Mauritania and Senegal.

An Orthodox church built by the Royal Family for the Russian community exiled to the French Riviera.

This massive blockhead sculpture hides an entire library.

A stranded woman lived alone on this remote island for 18 years, inspiring the great children's novel "Island of the Blue Dolphins."

An actual 1957 Cadillac De Ville, encased in 15 cubic yards of concrete.

A historic steam train meanders along one of the most scenic rail routes in Germany's Black Forest.

An antique narrow gauge railway line still running through the Colorado and New Mexico mountains.

Accessible only by boat, this centuries-old island fort never saw troops or combat.

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.

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

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

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

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

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.