Starokostiantyniv Castle has survived only partially. Once it was a powerful fortification, which occupied the whole of the broad cape formed by the confluence of Sluch and Ikopot rivers. The rivers washed the cape from the three sides, and from the fourth side there was a moat filled with water. All this made the cape with the castle an impregnable island. Along the perimeter of the island, there were earthen ramparts and 5-meter-high walls with five towers in the corners. In one of the towers there was a gate to which a drawbridge led over the moat.

A palace building situated on the riverbank has survived to this day. It is unique in its architectural design: the princely residence is fortified from one side by the defensive tower, and from another side it borders on the church.

The defense tower has an unusual bifurcated form. It is low and massive, but despite this, it is spectacularly decorated by the attic of the Renaissance style, which resembles a crown. The tower was designed primarily to defend the castle from the side of the river.

Starokostiantyniv Fortress was built in 1561 – 1571 by Prince Kostiantyn Ostrozkiy, who was a famous philanthropist, educator, and proponent of Orthodoxy. Thus, it is not surprising, that the princely palace is adjoined by the Orthodox church. The church is the only restored part of the castle and today it is the place of sacred service again. The fragments of the 16lh century paintings, dating back to the times of the Ostrozkiy, have been preserved there.

Kostiantyn Ostrozkiy founded not only the castle, but also the town of Starokostiantyniv, which was named after him. Starokostiantyniv was situated in the border, on the so-called Black Way, which Tatars used to advance on Podillia lands. That is why the town was thoroughly fortified with earthen ramparts and stone walls with towers. One could enter it only through one of three stone gates, which were well guarded.

To this day, only one of the city towers has survived. In the 18lh century, the tower was adjoined by a Polish Catholic church and the tower itself was turned into a belfry. The grim embrasures of lower tiers form a sharp contrast with elegant arches of the upper tiers, where the bells rang. Under the tower, there is an old cellar preserved.

Starokostiantyniv Castle successfully defended the town from many Tatar raids. The Crimean Tatars have never managed to capture it, even in 1618 when their 30,000 army invaded Podillia.

Often, Starokostiantyniv Castle found itself in the midst of popular uprisings. In 1593, under the walls of the town, the uprising led by Kshyshtof Kosynskiy suffered a crushing defeat. Another rebel, Severin Nalyvayko, was a centurion in Starokostiantyniv before he started the rebellion.