In 1793, during the last conversion, a chapel was created in the former tower rooms of the Bathhouse. The design was most likely prepared by Domenico Merlini. The current appearance of the Chapel clearly differs from the original one. Today, it is a small and fairly dark interior built on a rectangular plan, two storeys high, and lined with yellow and grey stucco – decorative marble-like material. The Chapel is framed with columns and pilasters with composite heads, which give the small interior an air of monumentality and gravity. Semi-circular windows extend above the cornice encircling the interior, and the construction is crowned with a cupola, which lets some light in. Soon after its construction the Chapel was ornamented with grey and purple stucco imitating porphyry. As a result of a flawed reconstruction conducted in 1922, the colour scheme of the interior was changed; its present appearance harmonizes with the decor of the central room of the Palace – the Rotunda. In the times of Stanisław August, a wood carved altar designed by Johann Christian Kamsetzer stood in the Chapel, however, it has been lost. Religious objects stored here included a crucifix, bronze candlesticks, and three kneelers. Currently, the equipment of the Chapel includes two pulpits shaped like chopped columns with marble counters. They were made by Domenico Bartoli in the scagliola technique, i.e. stucco decorated with inserts made of the same material, but of a different colour.