There is no treasure to be found here. All you see is filth. Dirty murky water and fumes rising from it burns your eyes. You see animals roaming around. Are they small dogs? No they are rodents, big rats. They glisten with the filth they are covered with. It is dark and difficult to see much else.
sewer entrance, Inside Tower
snakes
a rat chews on a dropped hymnbook
I stick to the edge, nose up and ready for any morsels that may drop my way. Or sometimes they don't, but I often don't know until my jaws are upon it. A hunk of moldy crust, the edge of a dropped hymnbook, it is all fair game.
Oh my, this tasty morsel?  It is so damp, moldy, and chewy, I can't  describe the euphoria of eating such a thing! Somehow I doubt it!  Where are you from?  No one could live in this filth forever! I grew up in this sewer, and I will die in this sewer, as did my ancestors. Have you heard of any treasures within this sewer?  I have looked about and have seen nothing. So many delicious things get dropped in this sewer!  Sometimes corpses get dropped in here to!  They are tasty too. But what about treasures?  Gold? Silver? Opals? or pearls? Those, what use are they?  Can't eat those! When a speck of sunlight touches them, they light up, or divert the light to other places in the sewer.  They may hurt your eyes, having only lived in the dark, but that is what I search for. You want to search for something that hurts your eyes?  All I want to do is eat tasty things!  I think the corpse that had this hymnbook had some shiny things on it though. Ahhh!  So, where is this corpse?  You must have moved the hymnbook as I can't see any of the bones here... Well . . . if you go down that sewer tunnel, keep on going strait past the giant pile of feces.  Then, take a left past the troll - he likes to sleep mostly.  There are some giant rats nearby as well, but they usually get killed by young adventurers.  Just a bit further and you will find the corpse.  He's a bit bloated and wearing a red robe. A red robe, you say... He may have many riches to be had!  How is the troll?  Will he be a problem?