Olyka Castle was the principal seat of the Radziwill princely family in Volhynia from 1564 until the late 18th century. The founder of the castle was Prince Mikołaj "the Black" Radziwiłł who gave Olyka to his youngest sonStanisław. Two senior branches of the Radziwill family were based in Nesvizh and Kletsk. The Olyka Castle was immensely influential as the first square fort with corner bastions in the Kresy and the prototype of many similar structures found in Eastern Europe. It was almost continuously under construction for eight decades and sustained numerous sieges between 1591 and 1648. It is one of the biggest castles in Ukraine, with 365 rooms. During Napoleon's invasion of Russia a Russian militaryhospital moved in and continued in use until 1837. An 1840 document refers to the castle as untenanted. In 1883, a campaign of restoration was launched but it was not taken to its conclusion until after the First World War. The Olyka Castle comprises four residential buildings of unequal height, forming a court in the middle and encircled by a moat. The towers of the original castle have crumbled to the ground, but the network of bastions is still in place. The main palace of three storeys, although originally built in the 16th century, is essentially the upshot of renovations carried out in the 17th and 18th centuries. Other buildings of the castle complex include a 17th-century gateway, a two-storey clock tower, and the Collegiate Church of the Holy Trinity, an elaborate replica of Il Gesu. During World War II, the Radziwill Fortress was the site of Nazi persecution of Olyka Jews in the Holocaust. As part of the Einsatzgruppen action of August 1941, 720 Jews were killed at the Olyka Castle and nearby. In July 1942, several hundred Jews perished in the castle. Monuments outside Olyka commemorate the place of execution of more than 4,000 Jews in Summer 1942 – in and around the Olyka ghetto, Radziwill Fortress, Olyka Castle, and surrounding areas. Israel's Holon Cemetery also has a monument in memory of the Jews of Olyka and its surroundings, who perished in the Holocaust. A psychiatric hospital, Volyn’s Hospital No. 2, is now located at the site of the Olyka Castle. The only part of the castle currently closed for visitors is a chamber for the Princes and their servants.
