The Renaissance Brežice Castle houses the Posavje Museum and its administration, galleries, storage facilities and restoration workshop. The museum’s collections encompass movable heritage from prehistoric to modern times, and paintings. The displays are well organized and beautifully presented.
On the first floor, there is a small auditorium, a gallery for temporary exhibitions and a historical display on the 16th century featuring documentary and archival material from the period of peasant uprisings and reformation in the Posavje region. The uprising of Slovene and Croatian peasants of 1573 is presented in a special display featuring presentations of several locations and the weapons of the noblemen and peasants. The Great Hall is the largest interior with Baroque murals in Central Europe. The murals were painted in the early 18th century by Karl Franz Remb (1674–1718). The Hall can be accessed through two entrances leading from the first and second floors. It is 35 m long, 10 m wide and 8 m high. The short sides feature wooden staircases, lavishly decorated with scroll motifs and portraits in medallions, painted in silver. The long sides are decorated with painted scenes of historical architecture, the short sides with landscapes, and the area between the walls and the ceiling with mythological scenes. On the ceiling, the painter depicted the sciences and arts. The murals on the walls depict paintings held by giants with putti above them (putto – a winged child).
The second floor can be accessed on a majestic staircase with Baroque murals painted in the early 18th century by Franz Ignaz Flurer (1688–1742). By means of painted architectural elements, the artist created a convincing illusion of infinite space in which he placed the most important protagonists of Greek and Roman mythology arranged around the central figure of Venus, the goddess of beauty and love. With the murals in the chapel, Flurer attempted to outdo Remb. He painted pillared architecture, vases and shells, all obligatory elements of the Baroque, on its walls.
The coats-of-arms of the Attems and Herberstein families are placed above the door. The rest of the chapel is arranged in the illusionist style, with paintings, like windows, leading the eye to vistas of infinity. The areas between the walls and the ceiling, and the ceiling itself, are covered with biblical scenes.
The archeological display consists of finds discovered in the local area. They date from the period between the Late Stone Age to the arrival of our Slavic ancestors and speak about an important chapter in the history of the Posavje region and the whole of Slovenia.
The modern history collection (1900–1945) features documentary material and objects from the Posavje region, covering the national struggles in the region, social upheavals in the period between the World Wars, and resistance against the occupying forces between 1941 and 1945. The material about the expulsion of Slovenes to concentration camps is presented in a special display.
The art historical collection consists of Baroque paintings. It can be divided into several important sections: religious art, landscapes, portraits, wooden Baroque sculptures and authentic murals in the rooms where the display is presented.
The gallery collection encompasses the permanent display of works by the painter and graphic artist Franjo Stiplovšek (1889–1963).