In my exploratory excursion via Google Earth of Florence for these Leonardo tales I found this cool alley... It took me to a place where I began imagining things from their perspectives. Again more research & there's speculation they found Leonardo's studio with hidden works off one of the piazzas.
 
I particularly love the compostion here as it is purely my own.  It also got me thinking into why narrow alley perspectives are so difficult and never look right.
 
This is revolutionary.  Out two eyes play a trick on narrow spaces by taking over the view of the opposite side. I haven't tested this yet. But the next time rendering a narrow space, I'm going to use two vanishing points. Each crossed opposite site by a small distance in the center of the sketch. It should widen the view just slightly by easing the vanish.