The Sears Tower in Chicago, Illinois. I have been to the very top of it before. Tis a long way down but a very cool view.

i think the twin towers, but now they're collapsed.

1) "Sears Tower is a 108-story, 1,450.58 feet (442 m) skyscraper in Chicago, Illinois. At the time of its completion in 1973 it was the tallest building in the world, surpassing the World Trade Center towers in New York. Currently, Sears Tower is the tallest skyscraper in the United States, and the fifth-tallest freestanding structure in the world. Although Sears' naming rights had expired in 2003, the building has continued to be called Sears Tower. However, in March 2009 London-based insurance broker Willis Group Holdings, Ltd., agreed to lease a large portion of the building and as part of the agreement obtained the building's naming rights. In summer 2009 the building will be renamed Willis Tower." Source and further information: http://en.wikipedia.org/wiki/Sears_Tower 2) "The 1,776 foot (541 m) 1 World Trade Center (previously known as the Freedom Tower), scheduled for construction on the former World Trade Center site, was intended to become the tallest building in the United States upon completion in 2010. The Chicago Spire (previously known as the Fordham Spire) a tower under construction in Chicago, Illinois is planned for completion in 2011. This tower would be taller than the under-construction 1 World Trade Center with a height of 2,000 feet (610 m) but it is now on hold, so it is uncertain which tower will be completed first." Source and further information: http://en.wikipedia.org/wiki/List_of_tallest_buildings_in_the_United_States Further information: http://en.wikipedia.org/wiki/List_of_tallest_freestanding_structures_in_the_world http://en.wikipedia.org/wiki/List_of_tallest_buildings_by_U.S._state