Hey!
Really nice mechanics and premise!
Just one comment:
I found myself never venturing too far from the entrance (actually only to the adjacent fields) so I would not get punished for delving too deep and having to run. Did I miss a rule to prevent this?
If not, I currently see 2 ways to make people delve deeper: Either rooms stay cleared and do not spawn new enemies, or enemies further away from the entrance give +1 extra gold for every field between their "room" and an exit.
Apologies, if I missed a rule here!