After visiting St' Francis Church and Monastery, I saw a sign regarding this Kastel . There is more inclined walking on cobblestones!
Entrance fee is 20 kunas, discounts for children and Seniors. A group of cannons had been laid in front of the Kastel. There are 2 museums inside: exhibits regarding the German Occupation and the other one is about boxing. Interesting combinations of exhibits here!
One can go around the grounds of this attraction to have a panoramic view of the city. Another option is to climb the tower for better views!