The St. Olaf Tower, also known as the main tower of Vyborg Castle, is a medieval donjon located in Vyborg, Russia. The tower was named in honor of St. Olaf, the Norwegian king who fought against paganism and was canonized by the church after his death. The exact date of the construction of the castle is unknown, but it is believed to have been built in the 1290s.

In the 1540s, the state rooms of the castle were covered with wooden panels for protection. By the middle of the 16th century, the castle was unable to withstand artillery fire and needed modernization. Under the leadership of German master Johann de Porte, construction began on the tower in 1561-1564 during the reign of King Eric XIV. The upper floors of the tower were dismantled and new brickwork was added on a stone foundation. The tower was transformed into a seven-story structure with a tetrahedral shape at the base and an octahedron shape on the upper floors to accommodate artillery. A hoist was installed on the fourth floor and a large aperture was made in the ceiling to lift heavy cannons and ammunition.

During the siege of Vyborg in 1710 by the troops of Peter the Great, the upper floors of the tower were destroyed by artillery fire. The tower also suffered damage from fires, including a lightning strike on the flagpole in 1834 and a fire caused by fireworks in 1856. In 1891-1894, the tower was given a new helmet-shaped dome and a granite porch at the entrance, and metal stairs were added inside the tower. link