Unit 731, the Imperial Japanese Army's covert biological and chemical warfare research facility at Pingfang district near Harbin in northeastern China (the colonial Manchukuo), operated from 1935 to 1945 and conducted among the most atrocious experimental programs of the twentieth century. Between 3,000 and 12,000 Chinese, Korean, Mongol, and Russian prisoners — called 'maruta' ('logs') by the Japanese researchers — were killed in vivisections, freezing experiments, forced pregnancies, disease inoculations, and pressure-chamber tests. The complex included a prison block, biological laboratories, a pathology museum containing preserved human body parts, and aircraft for aerosol-dispersion tests. The entire facility was demolished by retreating Japanese forces in August 1945; significant portions were subsequently unearthed and preserved by the Chinese government.
The site is today the Unit 731 Museum of Evidence of War Crimes. Chinese archaeological and paranormal researchers have maintained a formal incident log since the museum opened in 1985. Reported phenomena include voices in multiple Asian languages (Mandarin, Korean, Mongolian) heard in empty laboratory chambers, cold drafts in the preserved pathology-specimen wing, and the persistent impression on the part of night-watch staff of being addressed directly in dialects they do not speak. The restored prison block registers unusually strong phenomena, including in 2007 a formally-documented incident in which a Heilongjiang Provincial Public Security Bureau forensics team on routine security inspection reported hearing knocking from inside the sealed cell doors and a man's voice saying, in Mandarin, 'Please, let me leave.'
Unit 731's historical trauma — compounded by the post-war U.S. grant of immunity to the Japanese scientists in exchange for their data, which was used by the United States Army Biological Warfare Laboratories at Fort Detrick — has given the site a unique combined weight of historical horror and suppressed ancestral grievance. Chinese Buddhist and Taoist clergy perform annual pacifications at the site on August 15 (the anniversary of Japan's surrender). The site is formally protected as a national heritage location and is the subject of ongoing research under the Chinese Academy of Social Sciences.