The much-venerated monastery , Optina Pustyn , is close by . In the 19th century , this hermitage gained wide renown for its " startsy " . After the outbreak of World War II , a POW camp was established in the monastery for Polish officers taken captive by the Red Army during the Polish Defensive War of 1939 . Between April and May 1940 , the NKVD transferred approximately 5,000 of them to a forest near Katyn , where they were executed in what became known as the Katyn massacre . The remaining two hundred officers were sent to a camp in Pavlishchev Bor and then to Gryazovets . The town was occupied by the German army from October 8 , 1941 until December 27 , 1941 and was totally destroyed . It was rebuilt after the war
Katyn
Katyn massacre
Kozelsk