The Sanok Region Museum, established in 1934 as a community museum and designated a State Historical Museum in 1968, displays its collections throughout the halls of the Renaissance castle.

The castle building, erected by the starost Mikołaj Wolski between 1523 and 1548, with two wings added later, lost its original appearance over the course of its more than four-hundred-year history, succumbing to the needs and tastes of successive owners.
Archaeological excavations, source material and iconography have allowed for a partial reconstruction of its appearance, but it was only the major renovation of the castle building that revealed the internal divisions, the layout of windows and doors, and the stonework elements that had been hidden during numerous alterations and repairs, which were preserved and – where possible – reconstructed. In its heyday, the castle was a magnificent residence owned by the crown – specifically, it served as the residence of Queen Bona, whose ancestral Sforza coat-of-arms cartouche remains in the coat of arms of Sanok to this day. Along the perimeter walls, on both sides of the gate, there were service buildings – living quarters for the staff, stables, a coach house, an armoury, a kitchen, a bathhouse, a bakery and a brewery, the foundations of which have been uncovered during excavations that have been ongoing for several years. The well, which has survived to this day, was built during the tenure of Starost Mikołaj Wolski in the first half of the 16th century. The castle complex was built on a hill overlooking the San River, separated by its topography but closely linked to the town, which was granted town privileges whilst still part of Rus’ in 1339, and in 1340, together with the adjacent lands, was incorporated into the Crown. On the hill overlooking the San River stood a medieval stronghold with a castle, whose guests included: Casimir the Great, Władysław Jagiełło with his third wife, Elizabeth Granowska of Pilcza (after their wedding in Sanok), Cardinal Oleśnicki, whilst the following resided there: Władysław Jagiełło’s fourth wife – Queen Sophia (Sonka) and Queen Isabella of Hungary, widow of John Zápolya. The medieval castle (probably the northern part of the present building), defensive walls 4 cubits (2.4 m) thick, a massive stone Gothic tower from the time of King Casimir the Great, a brick tower, a drawbridge and moats – formed a formidable defensive complex, which was also an important strategic point on the Polish-Russian-Hungarian border. The presence of Romanesque elements within the Gothic architectural remains offers hope of dating the stone structures back further. Meanwhile, the burial ground, traces of earthworks, wooden residential structures, utility pits, and a large number of historic everyday objects and military artefacts uncovered during the excavations – document life in the early medieval fortified settlement, situated on a hill from the late 11th century. The construction and conservation work carried out in the 1990s made it possible to restore the main building largely to its 1558 appearance, which is fairly well known thanks to the surviving inventory. The castle cellars, accessed via steps from the courtyard, have been preserved in their original state. The cellars were of varying levels, with compacted earth in place of a floor. The wooden ceilings were replaced with stone vaults only between 1548 and 1558. At that time, the large cellars beneath the hall and the entrance hall were also divided by a partition wall into smaller ones, connected by a passageway with a stone portal. In the 19th century, the external entrances were filled in and the internal passages between the cellars were bricked up. During conservation work, for display purposes, the cellars were deepened and a brick floor was laid.