Great lake! I think you could obscure the underwater parts of the cliffs in that lake a bit more though, zoomed out it looked a little bit like a blue coloured pit. I'm loving the progress, especially around that central feature, it's just such a great example of how mapart happens I think.
"There will be a thing here"
"The thing here is a tree"
"Hmmm, actually it's a pillar"
"Ah, that's, what it was supposed to be. A lake!"
And then all of a sudden you get the whole underground realm too. It's like writing, when little things come out of your work and surprise you.

I like the poem a lot. Did I mention that yet? Lots of worthy discipline in your work here Wolram.

cheers,
Meshon