If you're looking for volunteer opportunities,
Preble Street is always welcoming help. Located in the
Bayside neighborhood, but only two blocks from Monument Square, there is a large
presence of social services organizations in this lower-income area. You don't see it in tour books or magazine articles promoting the city, but I would say that Portland has a pretty
sizable homeless population, especially per
capita.
Bonus picture from Oxford Street (just down the road from the above picture). I enjoy documenting sidewalks that are nearly impassable.