[good warriors always check their weapons first, yep. Zoro can't help but lean over to peer into the water, even though it's murky and all roiled up from their wading through it]

Ladders...

[oh wait that requires looking up. He scans the tunnel as far as they can see in either direction] No, doesn't look like it. Sewers usually have an outlet though, so if we follow the water we should come out eventually. Right? Water always flows toward the sea...