Two comments here. I would prefer more contrast between the levels (or walls versus floor if you prefer). Maybe smooth the textures on the floor more or increase the difference in color between the two? It seems to blend together too easily for my eyes.

In this section:

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Is this the entrance to the cavern, sloping down from above?

I like the subtle but still discernible grid. The colors remind me of a mine with high iron content, with yellow and red oxides staining the stone.

- Ernie