Krzemieniec is commonly associated with Queen Bona Sforza and the poet Juliusz Słowacki. Both figures were important both for the town itself and for the castle, contributing to its expansion or perpetuating the image of the fortress in literature. The centre had an early origin: there are reports from the second half of the 11th century confirming the existence of a defensive castle. Nearly a century and a half later, there was already a wooden castle of the Ruthenian dukes, which enabled effective defence against the Mongol invasion in 1240. The military value of the modest fortress was determined by its location (on a hill belonging to the range of the Krzemieniec Mountains), an invariable asset of the seat, which was subject to numerous modifications. The beginnings of the stone-built castle date back to the second half of the 14th century, when the estate was administered by Duke Lubart.

Under the rule of kings and grand dukes
. The development of Krzemieniec and the possibilities of expanding the fortress were conditioned by the ownership situation of the estate. In 1366 the centre was annexed to the Crown thanks to Casimir the Great, who at the same time took care of the security and smooth functioning of the city, providing the castle with a crew and bringing Polish officials. The king made the Lithuanian prince George Narymutowicz, a representative of the Gediminas dynasty, the direct host of the estate, which became a fief. Later, Krzemieniec was ruled by, among others, King Louis I the Great (Louis the Hungarian), Duke Lubart Gedyminovich (the aforementioned initiator of the castle reconstruction), as well as the brothers of the Polish King Władysław II Jagiełło: Skirgiełło, Witold Kiejstutowicz (uncle's brother) and Świdrygiełło. It was to the last of these dukes that the centre owed its municipal rights. A new stage in the history of the Krzemieniec castle began during the reign of Sigismund I the Old, who ruled the country in 1507-1548 - the starosty was then held by Queen Bona Sforza. The monarch's wife decided to modernise the defence system and rebuild the fortress, which took on a modern form.

The architecture and significance of Bona's castle
. The hill on which the complex was built was named Bona's Hill after the queen. Topographical conditions necessitated an irregular plan, making full use of the available terrain, with an entrance from the south-east. The perimeter walls reached up to 10 m high and 3 m thick. Modernisation in the first half of the 16th century included adapting the fortifications to the needs of artillery and the construction of a cistern to retain rainwater. The defence of the castle was supported by three towers - two on the eastern side and one at the end of the western tip of the walls. According to the information on the functioning of the castle in the 16th century, the stock of firearms in the castle was impressive (29 cannons, 10 hooks, 23 pistols, stocks of bullets and gunpowder). The castle lost its significance in the mid-17th century, during the Khmelnytsky uprising - the complex was then plundered and destroyed by Cossack troops, but the presence of the former fortress continually shaped the identity of the local population. Juliusz Słowacki, whose father worked as a teacher at the local high school, was born in Krzemieniec. The appearance of the town and the castle remained forever in the memory of the bard, who recalled the fortress in his hometown in one of his poems as follows: "There stands a mountain, baptised with Bona's name, Larger than the others - ruling the city with its shadow; An old - gloomy castle, which holds its forehead, Takes various shapes - clouds broken with a whirlwind; And during the day it looks with its blue shooting eyes, And at night, like a crown covered with a cirem of grief, Often moves the age-old chinks slowly, On the silvery moon rising on its face" (J. Słowacki, "Hour of Thought"). Although only relics have survived to the present day, the castle stands out in the landscape, towering over the town. The most legible fragments of the buildings are the perimeter walls and the entrance tower with a pointed archway.