During the 1997 and 2010 renovation of the Town Hall, an enigmatic structure was found below the north wall of the building. It was a cylindrical stone well, 3 meters deep and 2 meters wide. At first, it was believed to be a water tank. But the results of archaeological works beneath the floor of the structure excluded such a possibility. The permeable layer of sand could not hold water, as it was over 8 meters deep. No traces of waste nor excrement eliminated another potential function of the pit. Therefore it was assumed that the structure was a town prison, the dungeon.
The Town Hall in Tarnów has been rebuilt several times. Originally it was a standalone building of a weigh-house with an adjacent room, where a court sessions were held. It also served as a deposit of all legal documents and town seals. The actual Town Hall, where the Town’s Council meetings were held, was erected on the west side of original building, near the center of the Market Square. It was a separate structure made of brick, with a rectangular tower at a corner. The town prison was located between the two buildings. At the beginning of the 16th c. weigh-house and the Town Hall were joined with an “inlay” and the prison was incorporated into the foundations with use of a structural arch.
In the 1560s and 1570s, the Town Hall was thoroughly rebuilt and expanded, but fragments of the original walls were preserved. Beautiful Renaissance form of the building has survived until today, with just few minor modifications.
The archaeological findings from the dungeon, mostly fragments of a clay pottery, were reconstructed and are now exposed in the Town Hall.