Have you found the arm-wrestler? There's a door right next to him that will take you down into the sewers.
He hasn't made it that far in yet. I am trying to figure out how to explain it verbally. Can't find an image to use.
I'm so frustrated by this game, and this is the latest reason: I can't find the sewer location.
All these youtube videos and game guides on the netz say "in the city area." Okay, well, how do I get to the city area, hmm? Guards are everywhere. I'm running around in the general area were Iorveth tells me to either get arrested or find the sewers- the by the gargoyles and second rune chest, with a golem.
And I keep running and running and it all seems like an airtight system here, no real entrance to exit anywhere not covered by a bunch of guards.
There is a small room with a few people in it, sort of "above" where the golem is. Work your way in there, stearing clear of guards and out the back of that room is a ramp made from a fallen wall.
Getting arrested will get you in too. There is always that option.