The Posavje Museum Brežice, founded in 1949, has been part of the Posavje region for more than seven decades. The museum is rooted in a museum founded in Krško under the auspices of the Museum Society for the political districts of Brežice and Krško on 30th September 1939.

The museum is situated in the Brežice Castle (a national monument of immovable cultural heritage), in the town and municipality of Brežice, near the border between Slovenia and Croatia, in the Posavje region. The first castle was built in the 12th century by the Archdiocese of Salzburg. The current two-storey castle was built in the mid-16th century and was used as a residence by the Attems family during peaceful times. The Renaissance fortress contains one of Europe's most beautiful halls with frescoes: The Knight’s Hall.
The Posavje Museum Brežice is a regional museum, which presents the heritage of the Posavje region from the earliest days until today. Its permanent and temporary exhibitions are based on four collections: archaeology, ethnology, history, art history. The collections are also part of a series of interdisciplinary exhibitions ‘The Four Elements’: 1 – WATER, 2 – FIRE, 3 – EARTH, 4 – AIR.

The museum devotes special attention to accessibility, to various partnerships in the international arena with a focus on cross-border cooperation, to project activities, inclusion, to fostering the awareness of heritage and its worth, and to providing the opportunities for people to enjoy it.