A sleepy Austrian village may have hidden the ominous secret location of Nazi leader Adolph Hitler's plan to create an atomic bomb and win World War II.

A massive 75-acre underground factory complex, built by slave laborers and sealed with concrete by the Austrian government, has been discovered by Austrian filmmaker Andreas Sulzer, who believes it may be the secret site of Hitler's drive to make the world's first atomic bomb, The Washington Post reports.

The complex is located in St. Georgen an der Gusen, a tiny village of 4,000 and once the site of the Mathausen-Gusen concentration camp. Up to 320,000 prisoners from the camp, used as slave laborers, are believed to have died constructing the underground factory, connected to the B8 Bergkristall underground factory where the Nazis built the world's first jet fighter, the Messerschmitt Me 262, near the end of the war, the Post reported.

Sulzer got on the trail of the secret facility when he discovered documents, including a letter from a German scientist, Viktor Schauberger, who "was involved under the strictest secrecy in research projects for the SS in St. Georgen. In his letters, he talks about splitting the atom," the Post reported Sulzer said.

Further research turned up high levels of radiation near the site and Sulzer, funded by the German television network ZDF, began digging, Forbes reports.

The facility was "most likely the biggest secret weapons production facility of the Third Reich," Sulzer told the Daily Mail.

"Prisoners from concentration camps across Europe were handpicked for their special skills — physicists, chemists or other experts — to work on this monstrous project and we owe it to the victims to finally open the site and reveal the truth."

The industrial complex's location was long known, but Sulzer, who has been using ground-penetrating radar to map the underground area, believes a section where secret atomic experiments could have been conducted was missed and still remains hidden, the Daily Mail reports.

The site was commanded by SS Gen. Hans Kammler, who was in charge of Hitler's missile programs, and often visited by SS leader Heinrich Himmler, adding credence to the theory that top secret weapons research was underway.

"The SS leadership aspired to create a combination of missiles and weapons of mass destruction," Rainer Karlsch, a historian working with Sulzer, told the Daily Mirror. "They wanted to equip the A4 missile, or more advanced rockets, with poison gas, radioactive material or nuclear warheads."

The Austrian government has blocked further digging until Sulzer receives additional permits, but the filmmaker is confident that he will be allowed to proceed.

Sulzer "opened an important door that one has to go through," Samuel Laster, of "Die Judische" in Vienna, told The Jerusalem Post.