The northeastern tower of the Castle is preserved at a height of 4 to 8 metres. It was built by order of Vytautas (Vitovt) in the late XIV-early XV century and had the shape of an irregular square. The first floor is covered with a ribbed intersecting vault, the ribs of which are made of arrow-shaped bricks.
The tower was made without bonding with the Castle main walls and was made of cobblestone on lime mortar. There were made of brick the vaults, barrel-vaulted niches, and the arch of the tower entrance, and a passage in the thickness of the western wall was brick-dressed.
According to archaeologists, two niches in the southern wall were once used as fireplaces for heating the upper floors of the tower. The niches in the eastern and northern walls of the tower are compensator chambers.