I've been planning to create a mod adding a sewer system to all cities and some towns in Cyrodil, and a tunnel system to connect them. The mod is aimed towards bandit/Dark Brotherhood style characters and as such will not conflict with A Brotherhood Renewed (created by Arthmoor), but will not be compatible either unless written permission is given by the author. If anyone wants to help with this mod, post in this thread and PM me. The first stage of the mod will only involve the construction set. After the first release custom meshes/textures will be a possibility. Edit: Now that I think about it, I may at some point add in several different ways to travel across Cyrodil in relative safety for each of the guilds. The sewer and tunnel system takes priority, after this I'll either start with the mages or thieves guild depending on whether or not I have anyone familiar with blender working with me.