In den Arbeitslagern der Sowjetunion / In the labor camps of the Soviet Union
Link to the Arte topic page https://www.arte.tv/de/videos/RC-018530/gulag/Even the Russian tsars had political opponents perform forced labor in camps in Siberia. But in the Soviet Union, the camps took on a new dimension: The Gulag, the network of Soviet penal and labor camps, became a state within a state, whose existence was denied for decades. The prisoners were supposed to make their contribution to the "construction of socialism" there. Instead, many found death.
165 + minutes long documentary in 3 parts, online until 18/08/2021. (3 more days)
P.S. Sorry for the unfortunately very late linking, I have this topic on Arte overread.