CN Tower
"Guinness World Records" has called the CN Tower "the world's tallest self-supporting tower" and "the world's tallest free-standing tower". Although Guinness did list this description of the CN Tower under the heading "tallest building" at least once, it has also listed it under "tallest tower", omitting it from its list of "tallest buildings." In 1996, Guinness changed the tower's classification to "World's Tallest Building and Freestanding Structure". Emporis and the Council on Tall Buildings and Urban Habitat both listed the CN Tower as the world's tallest free-standing structure on land, and specifically state that the CN Tower is not a true building, thereby awarding the title of world's tallest building to Taipei 101, which is shorter than the CN Tower. The issue of what was tallest became moot when Burj Khalifa, then under construction, exceeded the height of the CN Tower in 2007 (see below).
Park Tower (Chicago)
Park Tower is a skyscraper located at 800 North Michigan Avenue in Chicago, Illinois. Completed in 2000 and standing at tall with 70 floors — 67 floors for practical use, it is the twelfth-tallest building in Chicago, the 43rd-tallest building in the United States, and the 83rd-tallest in the world by architectural detail. It is one of the world's tallest buildings to be clad with architectural precast concrete (the Transamerica Pyramid Building in San Francisco is taller). It is one of the tallest non-steel framed structures in the world—it is a cast-in-place concrete framed structure. This building was originally intended to be tall. But later, the ceiling heights were increased allowing it to reach .