A vast, winding sewer network runs under the Tenth District, lit by continual flame spells. Some of the tunnels are simply storm sewers, meant to carry rainwater and debris into great cisterns, where it is purified and sent into the pipes in the plumbing system that serves Ravnica's nicer neighborhoods. Others carry waste and refuse out of those neighborhoods, depositing it in different cisterns or dumping it into the undercity. Around the sewer system, smaller tunnel networks carry steam, distilled magical energy, and water to various places throughout the city. These passages are large enough for a humanoid to walk through but are often quite uncomfortable, filled with impure air and stifling heat.