The main theme of this thesis is the Doppelwendeltreppe, an example of twin spiral staircase situated in the Grazer Burg (Graz’s Castle) in the Austrian city of Graz. Through an historical research, typological analysis of the spiral staircases, constructive analysis of the case study and comparison with other example of spiral staircases both in Austria and in Italy, this thesis will try to analyse the object and understand it in its depth. Starting from the understanding of the urban layout of the city, going down to the scale of the historical city centre, passing to the Castle’s scale and then focusing directly on the Doppelwendeltreppe, this thesis shows how this twin spiral staircase is strictly connected to the history and territory of the city.