Also known as the Thai-Burma Railway and Kwai Railway. Immortalized in the David Lean film The Bridge on the River Kwai.

In 1943, the Japanese completed a railroad that ran through south Asia, to transport supplies for the war. Finished, it ran 415 km and was completed in just 16 months.

The Japanese used forced labor, in the form of civilians thorughout Asia (200,000) and Prisoners of War (68,000), to build and maintain it. Conditions were harsh. Laborers lived in huts with no roof. Cholera ran rampant and was not treated. The Japanese ignored the international rules regarding POWs. Officers were made to work. Laborers were often severly beaten for trivial or made-up reasons. Those that were sick were forced to work and often returned on stretcher, dead.

The prisoners were instructed to dig deep holes, to act as tank traps (in the virgin jungle, no less). Later evidence suggests the Japanese intended to use them as mass graves. A fuel depot nearby would be used to set prisoners aflame, and the charred remains would then be bulldozed over.

After the Japanese surrended, those at the railroad simply abandoned it, and did not even notify the prisoners. Prisoners awoke on August 18, 1945 to find the camp empty of Japanese. By the end, there were 96,000 dead prisoners, 18,000 of which were POWs.

Sources:
http://www.historyinfilm.com/kwai/fred.htm
http://www.bmw.ukf.net/3pagodas/