Augustinerkirche and the Herzgruft
The parish church of St. Augustin was the scene of numerous imperial weddings. It witnessed the marriages of Empress Maria Therese and Franz Stefan of Lorraine, Emperor Franz Joseph and Elisabeth, Crown Prince Rudolf and Princess Stephanie. It was also the scene of the proxy wedding (a common practice concluded before the bride traveled to her husband for the actual wedding ceremony) of Napoleon and Habsburg Archduchess Marie Louise. The Augustinian Church is also home to the Herzgruft where 54 Habsburg hearts are contained in silver urns ( Guided tours on Sundays after mass at around 12.15 and by prior arrangement).
Source: Wien Tourismus