Grimrock

I am thinking of creating a Tabletop RPG based on Legend of Grimrock, I have tried contacting Almosthuman for permission but got no reply, if anyone from AlmostHuman read these would they let me know if this would be a problem. I would be giving it away for free and all rights would stay with AlmostHuman.
Or if anyone else knows if this has been mentioned before I would be very grateful if you let me know.

Thanks

Quick forum search - here's something in German:
viewtopic.php?f=10&t=8331&p=84164