Tibbi, I don't remember exactly where I saw it, but in one of the staff releases, digging underground and making tunnels and basements was mentioned. It is in the works!
SECRET SEWER TUNNELS. Since it seems like home streets are going to be a fairly public thing, wouldn't it be awesome if people could put in secret sewer access tunnels in their basements or backyards as a more private means of traveling from one house to another?
PLUS tunnel streets would be AWESOME, especially if some of them came up into actual streets and some of them came up into subway lines so you could sneak past the ticket booth if you really wanted to, or use abandoned subway tunnels as secret meeting places, or .... it would just be awesome.