Great church built by Otto Wagner. The entrance fee (5 euros adults, 3 euros children) is definitely worth it.
From Wikipedia: The Church of “St. Leopold ”, better known as the Steinhof Church (or Otto Wagner Church at the Steinhof), was built in the course of the establishment of the Lower Austrian State Sanatorium and Nursing Home for the Nervous and Mentally Ill Am Steinhof from 1904 to 1907. The one in charge of the planning Architect Otto Wagner had to take into account that this is an institution church for mentally ill patients, and in discussions with doctors and nursing staff he determined the special requirements for such a building. A doctor's room, toilets and emergency exits were planned, the pews were not allowed to have sharp corners due to the risk of injury. Wagner, for whom the hygienic aspects were always a major concern in his projects, designed a variant with holy water dripping down instead of an ordinary holy water basin in order to reduce the risk of infections. He designed the floor sloping towards the sanctuary so that the patients in the back rows could see ahead better. In addition, there were separate entrances not only for the nursing staff, but also for male and female patients, as segregation of the sexes was mandatory in mental hospitals at that time. For lack of money, however, the Way of the Cross, the lower church for Protestants and the synagogue for Jews were no longer realized. Heating was also no longer installed.