The Biržai Regional Museum Sėla was opened on 16 February 1928 and has been operating in the restored Biržai Castle Palace since 1989. Some of the buildings of the bastion fortress complex have been restored or rebuilt.

The exhibition halls invite visitors to learn more about the history and culture of the Biržai region. The museum displays numerous archaeological finds testifying to the life of the ancient Baltic tribes of the region - sėliai and žemgaliai, as well as exhibits providing a good insight into the times of Counts Radziwill and Tyszkiewicz, the Biržai region during the reign of the Russian Empire, in times of independent Lithuania and in the second half of the 20th century. The museum also offers the opportunity to see many distinctive exhibits that prove the uniqueness of the ethnic culture of the Biržai region, the history of religious denominations, and the creative search and achievements of both professional and self-taught artists. 

The Arsenal features interactive exhibitions on the history of warfare and blacksmithing in the 16th and 17th centuries. Another visitor favourite is the exposition dedicated to the traditions of beer making, which presents lots of fascinating information about the processes of home brewing, the depth of traditional ethnic music and the hospitality of the Highlanders (aukštaičiai).