As a result of my boundless vanity, I occasionally check out from where the few hits of my blog come from. This doesn't take too long. The other day I noticed a few hits coming from a really interesting post by Joseph Manola titled "OSR aesthetics of ruin". It is a few years old, but I really recommend that you read it. I was busy cutting quotes from it to post here, but found that what I would have ended up doing was repeating almost all of it back to you. So read it!
So what I will add is that the comments Jean-Francois Lebreton recommends the paintings of life in the ruins of Rome by Hubert Robert and... wow! This stuff amazing - ripe for providing the visuals of a great FRPG setting. And, from this pointer, I found that there is a whole style of painting called Capriccio - "architectural fantasy, placing together buildings, archaeological ruins and other architectural elements in fictional and often fantastical combinations". I could see an entire OSR-game (or other game in which exploration was a key game 'mode') built around Capriccio.
View of the Port of Rippeta in Rome - Hubert Robert
A Capriccio of the Roman Forum - Giovanni Paolo Panini
Arches in ruins and Hecuba’s vengeance over Polymestor - Viviano Codazzi
And more, and more, and more.