St. Stephen’s Cathedral (Stephansdom) is the dominating symbol of Vienna, constructed between 1137 and 1147. It has four towers, and the 136.7 m high main tower (South Tower) was for many years the highest tower in Europe or worldwide, respectively. This chapter gives some historical information, geotechnical details, and describes the protective measures during the immediately adjacent Vienna Metro construction including a four-storey underground station connecting the Underground lines U1 and U3.