Which Is The Worlds Longest Building?

The Kansai International Airport's terminal in Osaka Bay (Japan) is the world's longest building. The total length of the terminal spans 1.7km and the airport is located on an artificial island. Due to the terminal's length, the airport does operate an automated people mover (APM) system to expedite the transport of people from one part of the massive building to another. The airport was opened in 1994 and is located approximately 50km from the city of Osaka. Thus far, construction at the airport has cost more than $15 billion and further expansion is on-going. In 2001, the airport's architecture won an engineering award from the American Society of Civil Engineers.

Kansai is Japan's second largest international airport. The airport served more than 15 million passengers in 2004 and the majority of these were international. In 2004, there were a total of 102,862 aircraft movements at the airport, but despite this seemingly high number, Kansai is actually underutilized.

While perhaps not the longest building, the SLAC National Accelerator Laboratory main LINAC building is much longer than the answer stated above.  The LINAC main housing building in 2 miles long (3.2km).