This immense—some might say immodest—neo-baroque cathedral opposite the former Royal Palace nods architecturally to St. Peter’s in Rome and served as the family church of the Hohenzollern dynasty up until 1918. The current building was completed in 1905 and has an interior every bit as dramatic as the outside. An outsize main hall features an ostentatious baptismal font, a mosaic by Guido Reni, and one of the largest organs in Germany, with more than 7,000 pipes. The crypt hosts almost a hundred burial monuments containing the remains of Hohenzollern royals and Prussian kings, notably Friedrich I and Sophie Charlotte. It's worth the climb to the upper dome, accessed via 270 steps, for memorable views across the adjacent Museum Island and beyond.