In 1988, during renovation works, the so-called Schneider's map was discovered, showing a handwritten depiction of a legendary tunnel leading under the Oder river.

[2] In 1288, Bishop Tomasz II founded a collegiate church near the castle chapel as an expression of gratitude for the hospitality received.

[1][2][5][10][11][12][13] This event was described by Jan Długosz in the Annals or Chronicles of the Famous Kingdom of Poland:[10]Gathering a large army, both from his own soldiers and mercenaries hired with monetary contribution which he levied on the Wrocław Church, he militarily invaded the lands of Duke Casimir of Opole and besieged the city of Racibórz due to the presence of Bishop Tomasz of Wrocław and his clergy there.

Touched by this, Bishop Tomasz, out of great kindness for which he was reputed, said: 'Rather let me and my clergy fall into the hands of the tyrant than these innocent people perish from hunger.

Let us, by our capture or, if it pleases God, by our death, avert the destruction threatening this city, which has sustained us for a long time and granted us refuge'.

And thus, wearing the mitre and the episcopal insignia, he sets out from the city with all his clergy in exile, to face the tyrant's camp, to appease his wrath with the greatest humility.

Bishop Tomasz, raising him from the ground, tearfully promised to forgive him all the apostasy he had committed, as long as he persevered in this contrition and piety.

Before leaving abroad, Count Karol Sobeck established in his will of 1739 a fund of 1,000 guilders for the castle vicar, who would receive accommodation and sustenance in the castle, serve in the chapel, and annually celebrate a requiem for all deceased subjects of the duchy, and established the feast day of St. John of Nepomuk (May 16) as a holiday for the entire duchy.

This fact is mentioned by Augustin Weltzel [pl]:[3]After the extinction of the Piast dynasty of the Opole and Racibórz duchies in 1532, they passed to the Austrian house as kings of Bohemia.

Although later, due to the sale, the castle was separated from the duchy, the emperor retained the patronage rights, and the hereditary owners received only demesne estates, but not the privileges of founders.

The last procession fell on the feast day of St. Marcellus I, the patron of Racibórz, and was established in commemoration of the foundation of the collegiate church.

[3][12][21] When the castle was owned by individuals of different denominations than Catholicism, such as George von Brandenburg, Jan Zygmunt Bathori, and Bethlen Gabor, masses could not be held in the chapel.

[8]By the end of the 16th century, the technical condition of the building had significantly deteriorated: the roof had not been repaired, the chapel had subsided, and the object, along with the sacristy, had numerous cracks, and the altars had collapsed.

[3][19] In 1670, through the efforts of George von Oppersdorff, the building was renovated, which, according to the land register, had been desecrated during the Thirty Years' War:[3][18][19][The chapel] completely deteriorated during the wars and became impure, but, thanks to the holy memory of Count George von Oppersdorff, it was restored in honor of Almighty God and St. Thomas Becket.

On 29 March 1688, Baron of Karol Gabriel von Węgierski and Countess Benigna Ester Praschma were united in holy matrimony by Scholaster Frederick Ferdinand Flade.

The county governor (Landeshauptmann) reported to the superior office (Oberamt), and on 26 June 1732, the emperor was informed by Count Franz Anton Schaffgotsch and Lazarus von Brunetti about the cessation of daily masses and annual processions, which were endowed in the castle chapel to honor St. Thomas Becket, depriving the local pastor of various incomes, which were taken over by the chapter.

Charles VI, or rather the highest chancellor of Czechia, Francis Ferdinand Count Kinsky, on 25 August 1733, summoned the royal superior office in the Upper and Lower Silesia duchies to demand from the members of the chapter a proper justification for why they had discontinued the daily services in the castle chapel against the literal content of the founding document and to present a relevant report as soon as possible.

[19] In 1873, a Neo-Gothic wooden altar of St. Thomas Becket, likely crafted by Adalbert Siekinder from Munich, along with a painting of the patron by Jan Bochenek and organs, were installed in the chapel.

On 3 June 2001, at 12:00 PM, after a long hiatus, a Mass was celebrated in front of the church, presided over by Father Jerzy Hetmańczyk, the parson of St. John the Baptist Parish.

Initially freestanding,[11] it is erected on a rectangular plan measuring 8.5 by 13 meters,[8] oriented, built of brick in the Wendish work, plastered, and has stone details from hewing.

Between the shafts in the eastern part of the north wall there are 3 niches, which are closed with trefoil and surrounded by richly profiled frames, the closures of which are slightly cantilevered.

[19][24] The lower level served as either the tomb oratory of Przemysław and his family or as a place for storing holy relics, functioning as a sanctuary.

The crypt under the chapel has a ribbed vault from the second half of the 17th century supported on two pillars and on chalice-shaped corbels located in the perimeter walls.

[4][16][17] Bishop of Wrocław, Tomasz II, founded a collegiate church at the castle chapel in 1288, where three canons and several vicars served.

[3] The bishop and the duke endowed the canon prebends with tithes collected from villages belonging to the Duchy of Cieszyn and Racibórz.

In 1308, Duke Leszek of Racibórz became the founder of a prebend from the altar of St. Margaret, and also transferred judicial power over the colonists living in the castle settlement to the canons.

When fourteen canonries were already established, the duke decided to request the bishop to transfer the collegiate chapter from the castle chapel to the parish church.

Although in 1416 the collegiate chapter was transferred to the parish church, daily Masses were still held in the castle chapel, and four times a year a solemn procession to honor the relics kept there took place.

Jan Długosz mentions Przemysław's piety in the Annals or Chronicles of the Famous Kingdom of Poland:[5]Each year, to honor him [St. Stanislaus] on his birthday, he [Przemysł] usually carried from Racibórz Castle to the Dominican monastery a candle so large that it exceeded his strength.

Since the dukes and lords changed their minds, he was buried in the Dominican monastery in Racibórz, to celebrate the feast of St. Stanislaus not every year, but continuously in the future.