Dachstein Stairway to Nothingness (Austria) – Visitors to Dachstein's Stairway to Nothingness must first cross Austria's highest bridge, which is 328 feet (100 meters) long and straddles a drop of 1,300 feet (396 meters). Then they face 14 steps that descend from the cliff face and which are surrounded by glass walls.

AlpspiX viewing platform (Germany) – The Alpspitze viewing platform comprises two steel beams, both of which measure 79 feet (24 meters) in length. Visitors brave enough to walk to the end of the glass-walled platforms can look 3,281 feet (1,000 meters) down into the valley.

Kinzua Skywalk (United States) – The Skywalk extends 624 feet (190 meters) into the Kinzua Gorge. Glass panels allow visitors to peer into the gorge below.

EdgeWalk CN Tower (Canada) – Located on the roof of the CN Tower's restaurant at a height of 1,168 feet (356 meters), the EdgeWalk in Toronto allows visitors to slip into climbing harnesses and walk around the edge of Canada's tallest structure. There's also a glass floor 1,122 feet (342 meters) above ground level, and although this glass is only 2.5 inches thick, it's strong enough to hold 14 hippos -- if they could fit in the elevator.

The Ledge (United States) – Visitors who step into one of the Ledge boxes in Chicago can see for 50 miles across four states. Six million people have ventured into the boxes since 2009, 500 people have proposed in them and visitors can now even get married in them.

7. Cliffwalk (Canada) – The Cliffwalk is a 700-foot (213-meter) walkway attached to a granite cliff face above the Capilano River in British Columbia. The highest point is 300 feet (90 meters) above the river.

8. The View from The Shard (England) – The Shard in London is the tallest building in Western Europe. The View From The Shard is located on floors 68, 69 and 72. The best panoramas are from floor 72, at a height of 800 feet (244 meters). This open-air observation deck offers 360-degree views of the city.

9. Stegastein lookout (Norway) – The lookout, commissioned by the Norwegian Highway Department as part of a project to improve the appearance of the country's tourist routes, allows visitors to look straight down into the Aurlandsfjord, 2,000 feet (609 meters) below.

Tokyo Skytree observation decks (Japan) – The Tokyo Skytree is the world's third-tallest structure, with a height of 2,080 feet (634 meters), and has Japan's two highest observation decks. The lower one is located at 1,148 feet (350 meters). The upper one, which has floor-to-ceiling windows and 360-degree views of the city, is perched at 1,476 feet (450 meters).

10. Top of Tyrol Stubai Glacier (Austria) – The Top of Tyrol viewing platform was completed in 2008 and provides visitors with spectacular views over 103 peaks. All of the parts -- including 19 tons of steel -- were lowered into place by helicopter.

Dachstein Glacier Skywalk (Austria) – The Dachstein Glacier actually comprises eight glaciers and a visit to this high-altitude, glass-bottomed walkway is a great way to see them all. On a clear day, the Triglav mountains of Slovenia and the forests of the Czech Republic can be seen.

Matteo Thun's Viewing Platform (Italy) – The best views of Italy's Merano region are from this binocular-shaped viewing platform, high above the gardens' huge oak forest. The viewing platform is just one of several within the gardens, which were recently named Italy's most beautiful gardens.

Grand Canyon Skywalk (United States) – This steel and glass, horseshoe-shaped walkway extends 70 feet (21 meters) over the lip of the Grand Canyon, almost one mile above the valley floor. Apollo astronaut Buzz Aldrin was the first person to step onto the Skywalk, which cost $30 million to build.