A guild city underlevel or sewer level would take significant planning and be pretty demanding. Personally my opinion is that we should just do a GUILD DUNGEON!! and do like Redrobes said and do our own dungeons and we'll (meaning Redrobes I suppose ) link em up at the end. It would result in a very interesting dungeon I think. Alternatively some people maybe can draw linking sections to make it work better together, but both those are after the fact considerations. I think that the dungeon one is just a fun and easy going sort of thing so would be more relaxed than one of the more intense Guild Projects.