The oldest building in Ostrog castle is the brick tower located at the southeastern end of the castle hill. "Tower" refers to the residential guard towers - the earliest and rarest types of towers that are created after the medieval towers prototype — the keeps. The Ostrog "tower" was used for various purposes and besides defensive purposes provided the conditions for the owners residence.
At the lowest lay of the tower various supplies were kept. A deep well was constructed here. The initial core of the tower plan is a south volume with a semicircular wall and almost square in the plan, the northern additional building. Later, in the late XV - beginning of XVI century southeastern part appeared. Along with the spatial development of the "tower" mighty buttresses grew in volume that flowed along the steep slopes and almost reached the foot of the hill.
The upper part of the "tower" is the result of later changes in XIX - early XX century. At the end of XVIII century the wooden top tier crowned with a large clock with "cymbals" (battle) was demolished.
35800, Ostrog, st.Akademichna, 5