Rosettes castle and Rocca Calascio

[Mark Knowles]

So Voynich castle may be originally inspired by some Italian castle (or several castles) but changed so much that trying to identify it would be wild goose chase.

Or it may be based on a castle which was destroyed and so no longer survives like the Castello di Porta di Giovia in Milan which was on the site of the now Castello Sforzesco and was destroyed in 1447 and on which I believe the illustration was based.