It housed St. John’s School, where Christoph Coelestin Mrongovius taught Polish in the period between 1812 and 1855. The popular name of “Mrongovius House” is misleading as Mrongovius lived elsewhere (on Kładki Street, Stare Przedmieście), and only taught at St. John’s School. The house managed to survive World War II. The surviving elements of the original decor include the portal and the top of the anterior facade.