What you call azulejos is basically tilings, which are mostly tiles with geometric patterns (or just a color) covering an area. Azulejo, in the "strict" portuguese (of Portugal) sense are usually a painting in the tiles (not on each individual tile, but on the whole). Mostly a work of art, yes..

By the way, there is also another "infrastructure" element that is used as art in Portugal - calçada portuguesa [1], which is also very interesting.

[1] https://pt.wikipedia.org/wiki/Cal%C3%A7ada_portuguesa