The Siesikai Manor castle stands on the southern shore of Lake Siesikai. Built in the early 16th century, it remains one of the earliest and most mysterious Renaissance buildings in Lithuania. Little is known about its supposed builder, Gabriel Daumantas Siesicki, but he is said to have been an enlightened nobleman who served Jagiellonian rulers – Casimir Jagiellon, King of Poland and Grand Duke of Lithuania, and his sons Vladislaus, King of Bohemia and Hungary, and Alexander, Grand Duke of Lithuania. However, in reliable and known historical sources Gabriel Daumantas (Daumantaitis) is mentioned only once – as a witness to the will of the nobleman Mikalojus Nemiraitis in 1471. In the mid-18th century Siesikai Manor was bought by Konstanty Daugiełło, the castellan of Ukmergė. This family held Siesikai Manor right up to nationalisation in 1940. In the mid-19th century the then owner of the manor, Dominik Daugiełło, rebuilt the castle, giving it classicist features. He assembled a large collection of works of art, historical artefacts and weapons in the palace. A small pagan shrine was also set up. Sadly, these treasures were lost in the turmoil of the 20th-century wars. The ground floor of the castle has been restored, and in 2024–2026 the authentic wall paintings on the upper floor were restored. Guided tours of about an hour are offered to visitors; the castle is a branch of the Ukmergė Local History Museum.