The Ostroh Castle is a castle in the city of Ostroh, located in the Rivne Oblast of western Ukraine. In the 14th, 15th and 16th centuries, the castle was the key stronghold of the powerful House of Ostroh. Today it is in ruins.
The first wooden fortifications were built in the area before the 1241 Mongol invasion of Rus, during which they were subsequently destroyed. The ruins were later reconstructed by Knyaz Daniil from the Ostrogky family on the city's Sudovy Hill (castle hill). Since then, more additions and reconstructions were carried out, although the complex still retains its Medieval architecture.
The castle complex consists of four main structures: the Guard Tower (Vezha murovana) where the castle's museum is located, the Bohoyavlenska Church, the New Tower, and the Belltower (constructed in 1905).