It's good, but if you really want to show off the depth perception, you need something to highlight the size of the different depth levels.

A simpler solution would be doors/archways/windows.

More complicated would be adding a texture, eg, stone tiles to a walkway.

Or you could you use people, but that would take a bit long to draw purely for defining distance.

That said, it still manages to convey an immensity. Is it underground? You may want to add clouds or a stalactite to highlight that.

That's all real good advice, thanks so much, I'll take all of these into account when I mess around with all this stuff at a later date!