In the old festival hall of the Romanesque palatial building from the 12th century, the Collection of arms is displayed. The collection is of national importance, since it consists of more than 500 pieces of various arms, ranging from cold steel arms, firearms, hunting and sport weapons, armours and other protective equipment from the 15th to 20th centuries.
The collection is designed in such a way that it resembles a real armoury, which was already there in the second half of the 17th century. Although the Ptuj castle used to have an important military role, its weapons have not been preserved. Most of the displayed arms come from the nearby Vurberk castle.