In 2006, on the corner of Solniční and Opletalova streets, directly opposite the Slavia Hotel, a drain and drainage canal was discovered at a depth of 6 metres. It was attached to the inner side of the fortification wall, which in that part took the form of a Baroque bastion system built in the 17th century.

The sewer, 1.7 metres high and 1 metre wide, was an arch of brick and plaster. The floor was also brick. The length of the sewer could not be determined, as two thirds of it was filled with sludge and clay. It was necessary to start with a gradual clearing. New information and discoveries slowly appeared. Many of the various connections and branching galleries were mostly filled with dirt and waste. This technical construction was made with great care and skill, but the long inactivity had left its mark. After cleaning, it was found that the tunnel continues in an eastward direction under the buildings between Opletalova and Česká Street and leads to Moravské náměstí (Moravian Square).

According to its location and archival documents, the sewer canal was probably built in the second half of the 17th century in connection with the construction of the new fortification of the city. This was confirmed by a dendrochronological analysis of a sample of the oak beams under the brick floor. The canal was in a recession two metres below the bottom of the medieval city moat for the purpose of draining wastewater from the surrounding buildings and probably from the city moat. Because it was also connected to the sewer leading from Špilberk, it also drew water from the surrounding slopes that used to feed the city stream. The drainage gallery is now accessible only through a hatch and shaft in the sidewalk on Česká Street.