Unidentified Earth 18 has at last been Identified: it's the municipal elevator in Oregon City, Oregon. This elevator is operated by the city of Oregon City (near Portland) as a connector between parts of the central business district that are literally separated by a cliff. I remember riding it once with my parents, when we went to Oregon City for some reason.
The identifying commenter, Seamus (whom I know as Shawn -- what gives?), wins all the Quatloos that would have been awarded to the people who have already identified Unidentified Earth 19. I guess that one was too easy.