The OSTROPA Souvenir Sheet was issued on 23 June 1935 to commemorate the Eastern Europe Stamp Exhibition (“OSTROPA”) in Königsberg, 23 June – 3 July 1935.

The four stamps depict:

• 3 Pf — Allenstein Castle over a map of East Prussia
• 6 Pf — Tannenberg Monument over an eagle
• 12 Pf — Königsberg Castle over East Prussian shield
• 25 Pf — Castle Heilsberg over an oak leaf

The purchase price for the sheet was 1.70 M.

This issue is difficult to find in great condition, as the original gum was very acidic, and if not removed, would degrade the sheet at a much faster rate than normal. Those which had the gum removed soon after issue tend to have whiter paper. The acid in the gum turned the paper brown over time.