Willis Tower Fast FactsBy CNN LibraryUpdated 6:28 PM ET, Sat May 31, 2014Scary viewing platforms 13 photosWillis Tower, Chicago – Visitors who step into one of the Ledge boxes at the Willis Tower in Chicago can see for 50 miles across four states. A protective coating on the glass cracked on Wednesday, May 28, but officials say visitors were never in danger. Click through this gallery to see more daring viewing platforms around the world:Hide Caption 1 of 13Scary viewing platforms 13 photosDachstein Stairway to Nothingness, Austria – Visitors to the Dachstein 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 surrounded by glass walls. Hide Caption 2 of 13Scary viewing platforms 13 photosAlpspix Viewing Platform, Germany – The Alpspix Viewing Platform features 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. Hide Caption 3 of 13Scary viewing platforms 13 photosKinzua Skywalk, Pennsylvania – The skywalk extends 624 feet (190 meters) into the Kinzua Gorge. Glass panels allow visitors to peer into the gorge below.Hide Caption 4 of 13Scary viewing platforms 13 photosEdgeWalk CN Tower, Toronto – 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.Hide Caption 5 of 13Scary viewing platforms 13 photosCliffwalk, British Columbia – 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.Hide Caption 6 of 13Scary viewing platforms 13 photosView from The Shard, London – 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. Hide Caption 7 of 13Scary viewing platforms 13 photosStegastein 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.Hide Caption 8 of 13Scary viewing platforms 13 photosTokyo Skytree observation decks – 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. Hide Caption 9 of 13Scary viewing platforms 13 photosTop of Tyrol, Austria – The Top of Tyrol viewing platform looks over Austria's Stubai Glacier, providing visitors with spectacular views over 103 peaks. Hide Caption 10 of 13Scary viewing platforms 13 photosDachstein 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. Hide Caption 11 of 13Scary viewing platforms 13 photosTrauttmansdorff Viewing Platform, Italy – The best views of Merano, Italy, are from this binocular-shaped viewing platform, high above a huge oak forest and the gardens of Trauttmansdorff Castle. The viewing platform is just one of several within the gardens.Hide Caption 12 of 13Scary viewing platforms 13 photosGrand Canyon Skywalk, Arizona – This steel and glass, horseshoe-shaped walkway extends 70 feet (21 meters) over the lip of the Grand Canyon, almost a mile above the valley floor. Apollo astronaut Buzz Aldrin was the first person to step onto the Skywalk, which cost $30 million. Hide Caption 13 of 13Here's some background information about Willis Tower, located in Chicago. Formerly the Sears Tower, it is now named for its tenants, the Willis Group Holdings.The visitors' observation deck, called the "Skydeck," is located on the 103rd floor.Other Info:The Sears Tower was the world's tallest building until 1996, when it was surpassed by the Petronas Twin Towers.100 tallest completed buildings in the world.With clear weather, four states are viewable up to 50 miles away: Michigan, Indiana, Illinois and Wisconsin.25,000 people enter the skyscraper every day.1.3 million visitors go up to the Skydeck each year.The Skydeck elevator can travel to the Skydeck in one minute, ten seconds.Characteristics:Structural Height - 1,450 feet or 110 floorsHeight with the two antennas - 1,730 feetHeight to Skydeck/103rd floor - 1,354 feetLowest level - 43 feet below Franklin St.Building Size - 4.56 million gross square feetWeight - 222,500 tons or 445 million poundsCost to build - $150 millionWindows - 16,100Building exterior - black aluminum and bronze-tinted glassArchitectural firm - Skidmore, Owings & Merrill Architect - Bruce Graham Structural Engineer - Fazlur KhanTimeline:1970 - Construction begins.May 3, 1973 - Construction is completed, the last floors are "topped out."1973 - The Sears Tower is open to tenants.1974 - The Skydeck opens to the public.1994 - Sears, Roebuck and Co. sells the building to Aldrich, Eastman & Waltch.1996 - The Petronas Twin Towers in Kuala Lumpur, Malaysia, surpass the Sears Tower in height to become the world's tallest buildings at 1,483 feet each. The Sears Tower becomes the world's third tallest building, at the time (behind Petronas Tower 1 and Petronas Tower 2). December 3, 1997 - AEW Partners LP sells the building to Canadian real estate firm, TrizecHahn Corp.August 28, 2003 - MIAC (Metropolitan Insurance and Annuity Company), an affiliate of MetLife, purchases the tower.March 2009 - The owners of the Sears Tower announce that the building will be renamed Willis Tower in 2009, after new tenant Willis Group Holdings. July 2009 - Skydeck's attraction, the Ledge, opens on the 103rd floor. It is a series of glass bays, with glass floors, that extend 4.3 feet outwards from the building. Visitors can now look directly down 1,353 feet to the street below.August 2009 - The Sears Tower is officially renamed Willis Tower.January 2010 - The Burj Khalifa in Dubai, U.A.E., becomes the world's tallest building measured at 2,717 feet, making Willis Tower the world's fifth tallest building, at the time.May 28, 2014 - Cracks develop in the protective coating on the Ledge attraction. Officials say no one was ever in danger. More from usAstronaut finds water in helmet after seven-hour spacewalk5 things to know for your New Day - Friday, February 27What color is this dress?