The RoyalTheater 1874. Longitudinal section by Jens Vilhelm Dahlerup https://www.rawpixel.com/image/8919263/the-royaltheater-1874-longitudinal-sectionFree Image from public domain licenseStudy of church towers at Petri Church and Church of Our Lady by Vilhelm Petersen https://www.rawpixel.com/image/8922202/photo-image-paper-art-vintageFree Image from public domain license