The difference between a work of architecture and a a work of art might be that the latter lacks of apparent functionality.
Therefore what, at first sight, might be perceived as architecture, insofar as it is not possible to fathom its use, then it should be considered as artwork.
This is, probably, what I had in the back of my mind, when I designed a bridge that cannot be crossed!
Or was it a tunnel with no mountain to drive through?
Precisely because the form is liberated from any practical use, it can be perceived in its purest essence.