The Abandoned Sewers (also known as Sewer Access in the SNES/PS version) is a location in Chrono Trigger that appears in the Future. It is the ruin of a structure built before the Apocalypse.
The Sewers are infested by Krawlie and his cohorts (Dondragos, Rats, etc.). Its the only way to get to Death Peak's continent by foot. The only way to get through is by walkways and bridges.
Several traps such as a fake Save Point and Cat spawn enemy battles here.
A letter found on the Sewers' bottom-most level complains about the inhumanity of the guillotine. Oddly enough, the letter only appears if Crono chose to rescue Fritz in the Prison Towers. Because of this, it is likely a descendant of Fritz wrote the letter to record the injustice his ancestor almost faced.