Under the town hall are historical cellars. Originally, there were 4 cellars with a direct entrance located in the southern wall of the town hall, near the eastern corner of the building. Before the last renovation of the city hall's underground, there were four cellars connected by passages. The primary construction materials used to build the cellars are layered stone and brick. Similar cellars can be found under the Franciscan Monastery, the library (former synagogue), the Starościński Building, the Corpus Christi Hospital, and many other buildings in Biecz. Among other purposes, they were used for storing barrels of Hungarian wine, an important trade commodity. According to legend, there is an underground passage connecting the castle with the Corpus Christi Collegiate Church. The corridor is said to lead all the way to the Franciscan Monastery.