Charles VI vowed a church while plague was killing Vienna in 1713, and Fischer von Erlach built him something no city had seen: a Greek temple portico, a Roman oval dome in green copper, and in front of them two colossal free-standing columns copied from Trajan's in Rome, spiralling with carved reliefs. Nothing structural required the columns. They were there to claim that this emperor's authority came down from ancient Rome, and they flattered him twice over, because the church is dedicated to Saint Karl Borromäus and the emperor paying for it was Karl VI. Every part of the design is borrowed from somewhere else, but no other church puts those parts together. A long shallow pool laid across the square in front reflects the whole facade, with a large modern sculpture set in the middle of the water as a deliberate counterweight.
Inside, everything pulls upward into the cupola, frescoed by Johann Michael Rottmayr with the patron saint rising through cloud. For twenty years a lift left over from restoration carried visitors up into the dome to see the brushwork at arm's length; it was dismantled in 2022, and the fresco is once again something you look at from the floor of the church, the way it was painted to be seen.