The Royal Castle in Sandomierz was built in the 14th century under Casimir the Great as a residence and fortress guarding the Vistula. During the Jagiellonian era, it gained Renaissance splendor with arcades.

In the 16th century, the castle served as a summer residence of the royal court, hosting nobility and dignitaries during important councils and feasts, emphasizing its prestige as one of the pearls of Jagiellonian architecture. However, the Swedish Deluge in the 17th century brought significant destruction, including plundering and fires, after which the building was rebuilt in Baroque and Classicist styles, losing its original character. After the partitions of Poland in the 18th century, it fell into ruin, serving as military barracks and a Tsarist prison, surviving numerous fires and neglect, becoming a symbol of the decline of former glory, yet retaining the status of a class zero monument requiring urgent protection and restoration.

After World War II, the renovation lasted almost 30 years, culminating in the Resolution of the Municipal National Council on June 25, 1986, transferring the castle to the Regional Museum in Sandomierz for perpetual use. Key works included the stabilization of the castle hill in 1998, comprehensive internal renovations in 2001, attic modernization in 2002, and a complete renovation of the south tower and knight's hall in 2004–2005, for which the museum was awarded the Sybilla 2002 prize in the conservation category. Today, it is the heart of the institution, housing permanent and temporary exhibitions, a Restoration Workshop in the cellars, and a knight's hall for conferences and concerts, reviving the medieval glory of Sandomierz for contemporary generations.