This paper discusses the adaptation of Rzeszow Castle in Rzeszow, Poland (also called the Castle of the House of Lubomirski in Rzeszow), which is a key building on the Subcarpathia’s map of monuments. The objective of the project was to identify the latest trends in conservation art, and, subsequently, to create a proposal for a contemporary interior arrangement for the castle and its site development. The aforementioned design work focused on creating new, innovative concepts for the revalorization of historical buildings, oriented towards development and modernity. The work presents bold, novel – and most importantly – workable solutions for a new functional programme for Rzeszow Castle. The main premise of the future modification of the monument was a complete change of use of the building: from administrative and office space (the current court) to a cultural facility with complementary functions. The proposals presented in the paper are aligned with new principles of cultural environment preservation, and primarily emphasize ideas that facilitate the development of culture and art, social engagement, and support new initiatives. The aforementioned new functional programme complements cultural facilities and events offered by the city of Rzeszow - the capital of the Subcarpathia Voivodeship (one of Poland's sixteen provinces). The article is based on thorough scientific and historical research. The characteristics of the building are presented, with focus on its architectural value, and the current state of preservation of the monument is described. The analysis of the functional-utility program became the basis for creating a contemporary and modern interior design. The final version of the interior plan was developed based on field studies and source research.