I like your use of cross-hatching and the design is a good use of space. The background texture and use of arrows are great touches.

I would recommend using a thinner line for your details inside the spaces (i.e. not the walls). The thick lines are great for your walls but I would recommend a different thickness for your elevations. Additionally you might consider some shading for your 'pit' in the room above the title.

As a personal preference, I would increase the lightness (brightness?) of the chambers to set them further apart from the background. Perhaps adding a white layer that's cut out to match your chambers and tunnels and set the opacity to like 20%?

Just a thought.

-GP