The Muzeum Warmii i Mazur (Museum of Warmia and Masuria) in Olsztyn is housed in the Gothic castle of the Warmian Chapter. To mark the centenary of the plebiscite, the museum prepared the exhibition “Wersal, plebiscyt i co dalej na Warmii i Mazurach?” (Versailles, the Plebiscite and its Aftermath in Warmia and Masuria), which tells the story of the First World War in East Prussia, the Treaty of Versailles, the plebiscite of 11 July 1920 and everyday life in Olsztyn between the wars. We prepared a mobile app with an audio guide to the exhibition in Polish and English. The recordings lead through four rooms – from mementoes of the 1914 Battle of Tannenberg, through documents and ballot papers from the plebiscite, to the history of the Tannenberg Monument – and the app also shows photographs of the exhibits with descriptions. For the museum we also created two touchscreen applications: “Stół wersalski” (The Versailles Table) with photographs and recordings, and “Głosowanie” (The Vote), in which visitors cast their vote and the results appear live on the museum's website.