Block canals are a network that stretches under old Krakow. These are the remains of the 19th century sewage system. It had two outlets: to the Old Vistula near St. Sebastian Street and to the Vistula River near Na Groblach Square. Only Śródmieście was channeled. The canals are probably 11 meters long and their condition often raised objections. In 1850 the main canal in Planty near Saint Michael’s prison collapsed. Today they are an obstacle to the restoration and maintenance of monuments. With the help of Silesian miners, the canals were examined and filled or replaced with special structures.