The main architectural attraction of the city of Ostrog is the prince's castle - a vivid example of ancient Russian defense architecture (5 Akademicheskaya Street). It was from here, on the remains of the ancient settlement, that Ostrog began its development. Its first wooden fortifications, built back in the pre-Mongolian period, were completely destroyed by the Mongol troops in 1241. However, in the first half of the next century, Prince Danilo Ostrozhsky restored the destroyed buildings on Castle Hill.
The castle began to be built in the 14th century. on a hill that towered 20 m above the surrounding area. The castle was ambiguous in plan, due to the peculiarities of the relief: it consisted of stone and wooden fortifications, surrounded by a moat with water. To our time from the complex of buildings of the castle have come down: the Murovannaya Tower (Vezha Murovana) of the 14th century, the New (round) tower, the 16th century, the Church of the Epiphany, the 15th-16th centuries, as well as the Lutsk and Tatar gate towers of the 15th - early 16th centuries ., which were part of the city fortifications and were important in the city's defense system. These and some other monuments are part of the State Historical and Cultural Reserve.
Today, the premises of the "vezha" are adapted for the museum of local lore. Archaeological finds, a collection of works of fine arts (Ukrainian and Polish paintings of various genres, a collection of Volyn icons starting from the 16th century), a collection of porcelain and faience of the 18th-20th centuries, arts and crafts (carved church utensils, icon cases, royal gates, rosettes) are kept here. , candlesticks, fragments of gravestones, portals, etc.). Of particular interest are the sculptures of Tadeusz Oskar Sosnowski.

A few meters from the walled vezha is the Church of the Epiphany. Documentary evidence of the time of construction was not found. According to indirect data, the first stone temple was built in the 15th century. The church is an example of a cross-domed structural system, widely represented in the architecture of pre-Mongolian Russia.