The sender is from the town of  Königswinter,but the card comes from Bonn. However,  Königswinter   has a legend about a dragon and that caught my attention. Königswinter is on the bank of the Rhine, across from Bad Godesberg. The Drachenfels is a hill between the two towns with the ruins of a 12th century castle, built by the Archbishop of Cologne. There is a cave in the hill that local folklore says housed a dragon. The dragon was slain by Siegfried, another figure is Germanic lore.