The Sewer Access is an underground network connecting the northwestern continent with the central continent. It's northern entrance is located on the northwestern continent just east of Arris Dome and south of Lab 32. It's southern entrance is located on the central continent to the west of Death Peak.
On a mission to open the sealed doors in 2300 A.D. after having been locked out of the Time Gate leading to 12,000 B.C., Crono's party returns to the Future and heads for the Sewer Access. Intending on just passing through to get to the next continent, they end up fighting and defeating Sir Krawlie. When they exit the Sewer Access, they push on toward Keeper's Dome.