The outer and inner castle system was developed in the 1540s. The passage between them was the Dark Gate which is still visible today. The outer castle was destroyed in 1702, but the gate continued to be used and was only walled up at the beginning of the 19th century.

By progressing further from the Dark Gate you arrive in the ground floor Barrack Halls, which provided effective protection against artillery attacks. The halls are now the venue for interactive exhibitions with multimedia elements presenting the story of the construction of the Castle’s gothic style Cathedral and the bishopric castle, as well as the military history and castle architecture in the era of the Ottoman occupation. The upper Barrack Hall hosts a popular exhibition, entitled "Eclipse of the Crescent Moon - the novel and reality".

From the Barrack Halls through the Gergely Bastion you arrive in the underground tunnel system built in the 1570s. These tunnels were constructed parallel to the castle walls, thus a safe underground passage was created between the bastions. The tunnels were also used for detecting enemy mines.