Some technical comments and corrections:
I really appreciated the "down to X" / "up to Y" indications on all the stairways. These are great and should be on all maps! However the one that says "Up to F10b" on the first floor map should say "Down to F10b", which caused some confusion.
The rents in the force field are underdescribed. How big are they? Does finding one completely negate the force field? Also, how far down does the force field go? Apparently it isn't meant to cover the engine level?
Where is the cloud? The giants in the engine level are supposed to fire at the PCs, yet the chains pass through the cloud and it is supposed to hamper the yaoguai. The art shows the engine level completely inside the cloud on p. 23, probably also on p. 8 (though in that one the bottom of the stone sticks out). If so, the giants firing downward are useless.
The GM should work out in advance which rooms have broken walls allowing access. My PCs flew around outside and it was hard to inform them--I missed one and they were annoyed. I believe they are F51, F54 and F56 (all trapped). Also it may help to know that F56, shown in an inset map, is (I think!) on top of F55.
GMs should be aware that a night attack makes it very easy for the PCs to bypass the whole ash-giant segment, as nothing will ever be able to see them. (The giants are "keeping a close eye" on the passage from over 500 feet away.) If you don't want this, I recommend lighting the whole cavern with pools and rivers of lava. Some lava "waterfalls" would be scenic!