I won't have you go a third time because my memory is what it is.
But if I remember correctly Beginner/Standard/Advanced are the default levels accessible in the menu, once you finish Advanced there's an Expert mode and that's the one I got stuck towards the end to never face again .... now don't go thru it once more 'cause the tedium of it all is aggravating and may as well loop you back in to A.
initial link at http://www.atari7800...chambersmap.htm
Read the text at the bottom of the pic, there's a new loop in Expert mode after Advanced is complete that I couldn't finish and I wouldn't impose onto you to try just to get disappointed once more or worse not manage to finish at 2 or 3 rooms from Z (happened to me).
I seem to remember that once you complete Advanced the Expert mode is even selectable on the initial screen (until power cycle that is).... once more unless you really are a glutton for punishment let it rest, my memory could be way off.
I actually enjoyed it quite some before noticing how boring it quickly becomes, such a pity. Not sure what they could have done to make it more fun though, I believe a little less raw monster count and some more strategy/level design could have been a step in the right direction.
EDIT: the whole mapping effort was documented here http://atariage.com/...-chambers-maps/
EDIT2: also if you play on a CRT via composite you'd see there's some use of artifacting/analog-blurring in the coloring of the halls while over SVideo it looks like weird dotted patterns on black