Everyone has heard of the concentration camps in Poland during World War II but this cover if from a different kind of camp.
At first glace it appears to be a normal field post cover from Zakopane to Aryes in East Prussia. However, it was sent from a K L. V camp - Camp Boleslewska.
The K.L.V (Kinderlandversichkung) were camps for sending children to in the countryside. On September 26th, 1940 Baldur von Schirach, head of the Hitler Youth (HJ) was ordered to organize a K.L.V. effort for the whole German Reich.
Initially, the evacuation of children applied only to Berlin and Hamburg. In addition to the Hitler Youth the BDM (Bund Deutscher Mädel), the group for German girls, helped to run the K.L.V. camps.
Shown here is a full letter from Gisela Eichoff to her brother who has become a reserve officer. It also mentions the attacks on Hamburg, which is probably why she is in this camp.