South Harbour
Lars, you find the warehouse that Nathan Lowduke is supposedly occupying without any trouble. It is perhaps a 5 minute stroll from the Bronze Trident, along the waterfront boardwalk. It sits nested between a fish monger and a rope maker, just as Marion explained to you.
You hide easily in the shadows across the street, managing to avoid most of the constant rain by an overhang from a nearby building. The warehouse has a broad set of heavy wooden double doors as its front entrance - a thick iron lock fastens them into place. The boardwalk runs along the side of the warehouse, towards the rear of the structure which appears to be suspended over the ocean on barnacle-crusted stilts. The building stands about 25 feet high and has a few windows running along its boardwalked sides (maybe one every 20 feet, and 5 feet off the ground). Some windows have been boarded up, but one or two have plate glass panes that have been opened slightly to let in fresh air.
Nobody comes or goes while you watch, but you can see dim lantern light spilling out from the open windows.