This is a brilliant game, well done!
Unfortunately, after playing through the game 2 times, checking the museum, and starting a new game after toggling some of the new starting options on and off, I got this error:
If Letters Had Pants error
ERR [string "code/ground.lua"]:1572: attempt to index a nil value
Stack traceback:
[string "code/game.lua"]:213: in function <[string "code/game.lua"]:197>
[string "code/game.lua"]:321: in function 'drw_level'
[string "code/game.lua"]:3097: in function 'drw_grid'
[string "code/ground.lua"]:1572: in function 'clear_dig'
This was on Win10, most recent version as of May 16th. You've got a great thing here, and I hope this helps make it better!