Vyborg castle, located on the Castle Island in the historic center of the city, is the most interesting tourist attraction of Vyborg. It has the characteristic features of a Scandinavian medieval castle, and from the observation point of the Olaf Tower one can have a magnificent view of the old town Vyborg.

The small island, previously known as the Oxen Island, is near the deep-water area of the Gulf of Finland of the Baltic Sea where it was possible to build a trade port. From the point of view of medieval fortification the island was a perfect place for building a strong castle. So, in 1293 the construction of the Vyborg castle had begun, and the Oxen Island was renamed the Castle Island.

Apart from the protection of trading routes, the Vyborg castle was also a strong bulwark against the spread of the influence of the crusaders on the lands of Karelia and Novgorod the Great. The troops of Novgorod more than once tried to capture the castle, but it remained impregnable.

To our time there survived the strong fortifications encircling nearly all Castle Island. Within the walls of the Vyborg castle there are several residential buildings and outhouses, but the central place is held by the Tower of St. Olav named so after the the king who baptized Scandinavia in the 11 century. This tower was both a watchtower and a war tower.

Around it in the Vyborg castle there were erected several outhouses and residential buildings surrounded by the wall with four corner towers: fire tower, watchtower, new tower and the tower of shoemaker. All these fortifications were built in the 15 century by the king Karl Knutsson (Bonde).

For the first time the Vyborg castle was captured by the Russian army of Peter I during the Northern War in 1710. Later, when the border was moved far to the west from St. Petersburg, and the Annensky fortifications were constructed in the Strait of Vyborg, the Vyborg castle lost its military significance.