During the time of the Galicia-Volyn principality, not far from modern Olyka, there was a fortified city of Chemerin, which had its own trading post. Over time, life from Chemerin gradually moved to this settlement, giving rise to a new settlement. The newly formed city was named Olyka on behalf of the river flowing nearby. The first owner of Olyka, in 1433, was Lenko Zarubich. Over the following years, Olyka changed its owners several times, until Jan Radziwill Cherny became its owner in 1547. He received from Emperor Charles V the hereditary title of "Prince on Olyka and Nesvizh", approved in 1549 by King Sigismund-August. So Olyka, for as much as 400 years, became the family nest of the Radziwills. It was the Radziwills who erected a castle here in 1558, which has partially survived to this day. The castle complex was square in plan and had four corner bastions with watchtowers. The remains of two of these bastions can still be seen behind the trees near the moats. In the first half of the 18th century, after repeated destruction, the castle was rebuilt and a palace was erected on its territory. Historical documents testify that the main gate of the palace was decorated with "indexes to astronomical compasses, as well as statues of the Mother of God and St. Michael with iron wings".
Next to the castle, according to the project of famous architects Benedetto Molli and Giovanni Maliverna, the majestic Trinity Church was built, which has survived to this day. The entrance to the city was decorated with the Lutsk Gate, which still greets residents and guests of Olyka today. After Olyka joined the Russian Empire in 1793, life in the city began to subside. The reason for this was the great fires of 1803 and 1823, as well as the war of 1812. Then the estate was turned into a military hospital, which operated until 1837. And today, in the former family nest of the Radziwills, there is a medical institution - the Volyn Psychiatric Hospital. In the daytime, you can freely enter its territory and see the former grandeur of the palace. The last of the Radziwill family, who lived in Olyka, was Janusz Radziwill, who was arrested in 1939 by the NKVD, after the entry of Western Ukraine into the USSR.