We (as in most academics and I wouldn't really call myself one) believe Shakespeare did not travel outside England. He read a lot and enjoyed the visits of the guilds who travelled putting on plays.
So, how did he know about Rome, Venice, Denmark, Scotland, Verona, Athens, Greece, France, Germany, etc etc?
When I look closely at his plays set in those places OR which mention those places, it's not the landscape, not the flora or fauna which he mentions - rather it's all about CHARACTER. Characters and their relationships. Themes pertaining to this subject which are universal - they traverse time and space.
So, I am being a bit hung up trying to ensure authenticity (such is the demand - and rightly so - of today's readers) but I keep reminding myself that it's about the story.
And the story? Fleance's quest to find ultimate happiness in a world which brings him challenges.
Loved this from the Children's Book Council of Australia: Shakespeare constantly raises philosophical, ethical and moral questions. Banquo's Son challenges us in the same way through the 'novel' form as distinct from the 'play'.