Hinged mailbox key holder that looks like a mailbox. With double-sided sticky tape, affixes to the wall (careful about the wall paint with the really strong tape, I wasn't).
After printing, you can slide one peg into deep into one side and carefully slide on the other. Worst case is to file the holes (not pegs) a tad to make them fit.
Due to the size, the pegs are a tad fragile - but I think it will last a while.