Hey Feanity,
That is actually the entrance room for the level and the shape you see is the light from the room above. There should be a room with a hole in the center. The dungeons are randomly generated so there is a small chance that the floor that generated for you didnt have a way out. I tried to really prevent this and hope it was just a bit hard to see. I'll check it out though and try and recreate it. Going back in to the cave should fix the problem,
Thanks for the feedback,
Rafi