The archdeacon's library first opened in 1793. It currently boasts over 130,000 extremely rare books including Medieval manuscripts, incunabula, 16C, 17C and 18C works and the only letter written by Mozart on Hungarian soil. The painted ceiling, the work of Johann Kracker in 1770, is one of Hungary's most famous frescoes. Also worth visiting are the observatory, home to a small astronomical museum and the Camera obscura which offers an insight into the mysteries of the darkroom.