We visited this lovely cathedral on a tour with AMAWaterways. We had a great guide who added to the historic information that I had read prior to the tour (highly recommended).
St. Stephen's Cathedral is the mother church of the Roman Catholic Archdiocese of Vienna and the seat of the Archbishop of Vienna. The current Romanesque and Gothic form of the cathedral was largely initiated by Duke Rudolf IV (1339–1365) and stands on the ruins of two earlier churches, the first a parish church consecrated in 1147. Its multi-coloured tile roof, become one of the city's most recognizable symbols.
During World War II, the cathedral was saved from intentional destruction at the hands of retreating German forces when Wehrmacht Captain Gerhard Klinkicht disregarded orders from the city commandant, "Sepp" Dietrich, to "fire a hundred shells and reduce it to rubble".
Built of limestone, the cathedral is 107 metres (351 ft.) long, 40 metres (130 ft.) wide, and 136 metres (446 ft.) tall at its highest point. The glory of St. Stephen's Cathedral is its ornately patterned, richly coloured roof, 111 metres (364 ft) long, and covered by 230,000 glazed tiles. On the roof, above the choir on the south side of the building the tiles form a mosaic of the double-headed eagle that is symbolic of the empire ruled from Vienna by the Habsburg dynasty.
This is definitely a "must-see" on your visit to Vienna.