In which of these countries is Biržai Castle?

Biržai Castle (Lithuanian: "Biržų pilis") is a 16th century castle in Biržai, northern Lithuania. It is located in Aukštaitija region, Panevėžys County. The castle was the first Italian-style bastion fort in Lithuania and one of the first in North-Eastern Europe. The well-preserved castle (most recently restored in 2013) now houses a museum, a library and a restaurant.

Construction of the earth bastion-type castle started in 1586 by the order of Krzysztof "Piorun" Radziwiłł. In 1575, preparing for this construction, a dam was built on the Agluona and Apaščia rivers at their confluence, and the artificial Lake Širvėna, covering about 40 km2 (15 sq mi), was created. Major works were finished in 1589.

Since the second half of the 17th century, the castle has been the main seat of the Biržai-Dubingiai Radziwiłł family line, which was transferred here from the Dubingiai Castle. Biržai Castle served as an essential Lithuanian stronghold during the wars with Sweden.

The castle was reconstructed from ruins in the 1980s, in the Renaissance-Baroque style. The residential manor of the castle houses a library and a regional history museum "Sėla" (literally Selonia), founded in 1928.