You don't have to go to the verdistis area, but you must join the thieves guild so you can get the key to the sewers from the poor quarter, you can always use the market sewers, but this is a much longer route, and it will be much more difficult as you get the locations from Rob (the guildmaster of the thieves guild) and the lock in the prisons (past the torture chamber) can't be picked, I don;t know what's behind them either, sorry.
