It is one thing to describe a place, another to describe a place as it was. I think visually, so maps, drawings, art are usually my first stop in coming to grips with a story location.
(Top image is a view of Florence by Hartmann Schedel, ca. 1493.)
I cannot find a date for the map above, only a notation online that the highlights are the walls and fortifications circa 1500. However, it seems plausible—? It's times like these that I keep reminding myself, I'm writing fantasy, I've got people who live on blood and serpent gods and alchemists chasing immortality; I remind myself that it's about the story first and foremost, not nailing the precise logistics from A to B. (And that I cannot afford, financially, to undertake as much research as I would like.)
It's challenging, but it's also one of the intense pleasures of writing this series: trying to enter into different times and places, letting myself wonder what the world was like then. Even as I recognize the terrible conceit in trying to recreate a possible 15th century with my 21st century mindset, it's an awful lot of fun.