Ostroh Castle, Medieval defensive castle in Ostroh, Ukraine.

Ostroh Castle stands on a 20-metre hill above the Viliya valley in Ostroh. Its surviving ensemble comprises the Murowana Tower (14th c.), the Round Tower (16th c.), the Epiphany Cathedral (15th–16th c.), the 1905 gate bell tower and wall fragments. The Murowana Tower is a three-tier structure of sandstone and brick with 15th–17th-century buttresses.

After Mongol forces destroyed wooden fortifications in 1241, the Ostrogski family acquired the town in the late 14th century and built the stone castle. This construction marked the shift from temporary to permanent defensive structures in the region.

The Guard Tower houses the Ethnography and History Museum, while the Lutsk Tower functions as a museum dedicated to the history of book printing.

The castle stands on a 20-metre hill above the Viliya valley, with the Murowana Tower in the south-east and the Round Tower in the south-west. The museum inside the Murowana Tower has operated since 24 August 1916. The gate bell tower dates from 1905. Expect uneven ground and narrow stairs between the towers and the Bohoyavlensky Cathedral.

The castle stands on Sudovy Hill above the Viliya valley, on the site of a wooden fort destroyed by Mongol forces in 1241; the stone castle repeated the layout of the older hillfort. The 20-metre hill and a water-filled moat were part of its defence. In the small park outside the walls, a monument of 1978 marks 400 years since the founding of the Ostroh Academy.