Access the sewers beneath GCPD | Main storyline Batman: AO Guide

The entrance to the sewers is in the Northern part of the Burnley district yet, it is not that easy to locate it. Go West of the marker set by the game (screenshot 1), thanks to which you will find a small area between buildings. Reach here the lowest level to find the sewer's entrance shown in screenshot 2. Go ahead and note, after a moment's march, the manhole to the Western sewer section [Burnley Sewers - West].