Trinity monastery-fortress is considered one of the best medieval architectural ensembles in Ukraine. The decoration of the monastery is the Trinity Church, in which the icon of the Mother of God of the 16th century has been preserved. Near the fortress walls there is a large old stove - near it on winter nights in the Middle Ages the guards guarding the monastery warmed themselves.

The village of Mezherichi is a suburb of Ostrog, a district center on the border of Khmelnitsky and Rivne regions. In historical documents, Mezherichi was first mentioned in 1386, due to the fact that the Lithuanian prince Vitovt confirmed the right of ownership of the settlement to Fedor Ostrozhsky with his letter. It was F. Ostrozhsky who erected a castle in Mezherichi, which at first was wooden. In the XV century. Vasily Ostrozhsky surrounds the castle with stone walls. A few years later, his son Ivan built a wooden Trinity Church on the territory of the fortress, which was destroyed by fire in the middle of the 15th century. At the same time, on the site of the conflagration, the construction of a stone Temple began, which has survived to this day.
Simultaneously with the construction of the new Trinity Church, work began to strengthen the castle. It is surrounded by earthen ramparts, with a total length of about 2 km. In the middle of the XVII - beginning of the XVIII century, as a result of the Cossack uprisings, the castle was significantly damaged. After the restoration of the castle, a Franciscan monastery is located within its walls. On the northern and southern sides of the church, two two-story premises are added, in which residential and auxiliary premises are located. Round three-tiered towers with loopholes on each tier were built along the four outer corners. The castle has been well preserved to this day. Now it houses the Holy Trinity Monastery. It has recently undergone renovation work.