Pejačević Castle in Osijek is a cultural heritage building that represents the architectural achievement of an unknown architect, providing testimony to the rich cultural history of Osijek and the entire area of Slavonia, which has been almost entirely neglected in our history. It was built in 1801 in the style of baroque classicism which was a common style of architecture during that period. By the castle, there used to be a big park which, together with the funerary chapel and the castle, created a unique ambience. During its long history, the castle has had many different owners and purposes. Therefore, there have been many changes, mostly in its interior, while the exterior of the building has remained almost the same. This paper deals with the historical development of this imposing building, from its construction to this day. It includes all the conservation-restoration work carried out so far, the current condition of the castle and a personal review of the present-day function of the building as well as the possibility of its revitalisation.