A new low, even for a villain, you've stumbled through the very very bottom of Grandville in the area known as 'The Gutter.'
The Sewer Dweller Badge marker is located in The Gutter neighborhood of Grandville. It is on top of a sewer pipe located 216 yards northeast of The Gutter marker.
Its coordinates are (2682, -443, -731).
Gladiator Badge Unlocked
When you obtain this badge, you will unlock the Arachnoid gladiator badge.