[Acme]

About the best I can come up with are these:

Map of Steam Tunnels under U-Dub.  I could see these get co-opted depending on how far the OU expands.

A picture someone has in their Flickr of an old Seattle Map I'm assuming the Red section is the places that were rebuilt over since the guy tagged it with Seattle Underground.

A general map of Pioneer Square, deliniating the Historical District

I think the biggest problem is that the Seattle Government may have actively suppressed a map of the SU from getting anywhere but the files and archives to keep people from exploring and getting hurt or finding a new way to break into some building.  The Underground Tour sure isn't helping, because that's their cash cow and of course they want to keep it pretty much to themselves.