We entered this buried river through the outfall outside the city. Shortly after entering we where rewarded with many types of brick and stone tunnels. Even some parts reinforced with steel ribs.
A particularly old part was found behind a small tunnel.
It turned out to be an disused sewer tunnel which used to connect to old rooms, locally known as the catacombs. Sadly the passage is closed these days. We had no way to go but follow the main tunnel.
After a while we found another level which also used to connect to the catacombs. Sadly no entry here either.