Belzec, was the first of the Nazi German extermination camps created for implementing Operation Reinhard during the Holocaust.
Operating from March 17, 1942 to the end of June 1943, the camp was situated in occupied Poland about 1 km south of the local railroad station of Bełżec in the Lublin district of the General Government.
Between 430,000 and 500,000 Jews are believed to have been killed at Bełżec, along with an unknown number of Poles and Roma; only one or two Jews are known to have survived Bełżec and the war: Rudolf Reder and Chaim Hirszman.
The lack of survivors, who could have given testimony, is the primary reason why this camp is so little known despite the enormous number of victims.
An article about Operation Reinhard in swedish Wikipedia. The construction of Sobibor, Treblinka and Belzec exterminations camps with further links to other languages.