Made globally famous by a creepy 2015 viral video, the history of Zofiówka Sanitorium, 23km south-east of Warsaw in Otwock, is harrowing to say the least. Built in 1908 by the "Society for Poor Jews with Nervous and Mental Illnesses" (PL: Towarzystwo Opieki nad Ubogimi, Nerwowo i Umysłowo Chorymi Żydami), this facility was part of a new approach to the institutionalised treatment of mental disorders. The Nazi invasion of Poland in 1939 saw Zofiówka become part of the Jewish Ghetto in Otwock, where some 400 patients slowly starved to death. When the ghetto was liquidated in 1942, another 100-150 patients were shot and the rest were sent to Treblinka. Only a few Zofiówka doctors survived the Holocaust, with some staff committing suicide and all of the patients perishing. In the last two years of the war, as part of the Nazi Party's policy of Germanisation, the facility served as an orphanage for Polish children who were waiting to be passed on to German families. During the communist era, Zofiówka returned to its function as a mental health facility, primarily for young people. From 1985 the facilities were used to treat neuropsychiatric disorders associated with drug addiction until the mid 90s, when it was finally closed for good.
If you get a skin-tingling thrill out of trespassing in abandoned and dilapidated places (at your own risk, of course), Zofiówka will be right up your alley. The facility is, of course, best visited after dark, when the tortured spirits of the facility tend to make themselves known!