How about something related to history and outer East Portland? I think that there's some interesting history out there that is left untold or at least under-appreciated. Agriculture, post war neighborhoods, the Kelly Butte Civil Defense Center, the Mt. Hood Freeway. I'm sure there are plenty more that could be woven into a tour of some sort.
I was recently reading about "The White House," a hotel/booze joint/possible bawdy house that was on the west side of the Willamette, across from Milwaukie. It burned to the ground many decades ago. I'm not sure if any trace is left or if it's on private land or what. For a while Macadam was apparently called "White House Road." I'll have to do some research.