I'm reading the second book of Hugh Thomas's trilogy about the early Spanish empire. He mentions a Flemish artist named Anton van den Wyngaerde who "sketched most of the towns of Castile - so carefully that in 1572 he retired to Madrid with his hands crippled."
That made me curious, so I looked him up. His are the best city panoramas I've ever seen. While reading about Florentine history I naturally wanted to see what old Florence looked like, and the best that I could find on the Internet was this. Wyngaerde's stuff is better. This is just beautiful, as are this and this.
Whenever I look at walled cities or castles, I immediately imagine them being taken by an army. The best cinematic portrayal of that I have seen is contained in Andrei Tarkovsky's movie Andrei Rublev.
There is an album of Wyngaerde's sketches on sale. I'm guessing that there's more stuff there than is available online, but I haven't yet decided if I want to splurge on it.