The NASA Vehicle Assembly Building from behind.
The Vehicle Assembly Building (VAB) is one of the largest buildings in the world. It was originally built for assembly of Apollo/Saturn vehicles and was later modified to support Space Shuttle operations. High Bays 1 and 3 are used for integration and stacking of the complete Space Shuttle vehicle. High Bay 2 is used for external tank (ET) checkout and storage and as a contingency storage area for orbiters. High Bay 4 is also used for ET checkout and storage, as well as for payload canister operations and solid rocket booster (SRB) contingency handling. (Source: http://science.ksc.nasa.gov/facilities/vab.html )