Photos displayed inside this Unesco World Heritage site attest to how dilapidated the cathedral was until the early 1990s – the original dates back to 1333. The lofty interior is dominated by an ornate organ used for regular concerts, which are well worth attending. Upstairs, the carved-wood Wallenrodt Library has interesting displays of old Königsberg.
The top floor is devoted to noted philosopher and Kaliningrad native Immanuel Kant (1724–1804); the exhibition includes his death mask. Kant's Tomb is on the building's outer north side.