"Auf den Inseln" ("On the islands") is the first exclusive German Cthulhu campaign. It contains three scenarios plus a vast amount of background information on the german north sea coastal areas covered by these scenarios, especially the islands Borkum and Sylt.
From publishers website (translated):
Product info: Besides the voluminous campaign book "Auf den Inseln" contains several full-colour historical maps, e. g. maps of the islands Borkum and Sylt plus an general map of the whole german north sea area. Also included in the box are booklet with frisian myths and legends, which can be utilized in the campaign and are specially fitted for the scenarios, and a reproduction of a 1920s tourist guide for Borkum island. For the gamemaster's use there's every handout used in the scenarios included separately and in colour.