I started mapping out my quest to the bottom. i got to 13S, and could get further if i didn't get myself stuck at 5E/13S! i keep going east, i still haven't even seen 4W/11S...
solid lines are impossible to pass by solid level gen, dotted lines are where i'm pretty sure the path is permanently blocked by bubbles. numbers are my loose measure of clutteredness/difficulty.
p.s. i agree about "North", "south". but i think they're probably more universally understood as single letters than U/D? i had briefly considered "3F" vs "B2" for up and down.