Mniszek
In a forest about seventy kilometres northeast of Bydgoszcz, the Nazis murdered about 10,000 poles between November 1939, and January, 1945. The majority of the victims had been murdered as part of Aktion AB (Ausserordentliche Befriedungsaktion), which aimed to murder educated Poles whom the Nazis considered to be potential leaders of a Polish resistance movement. The victims came from Chelmno (not to be confused with the extermination camp with the same name), Grudziadz, Bydgoszcz, Starograd and from the mental hospital in Swieciu.
Current status: Monument (2012).
Location: 53°28'58.9"N 18°37'17.7"E
Get there: Car.
Follow up in books: Lukas, Richard C: Forgotten Holocaust: The Poles Under German Occupation 1939-1944 (2008).
The site is located about 1.5 kilometers from the main road onto a forest road in bad condition. But the site itself is located in a large pit, well maintained and surrounded by a number of monuments. Right at the memorial entrance there is a seemingly meaningless little enclosure around a tree. But if you look at the tree a little closer, you can see rough nails in which the Nazis attached ropes that people were hanged from.