I've heard the term “Narnian” used in different ways. I've heard it used to describe something bizarre, mysterious or interesting. But when I was reading it, I interpreted it as something other-worldly, fantasy-like or whimsical.
I read the references the poet gave, and I went to the place she described. The staircase was interesting. Just as the poem says, you wouldn't expect it to be there.

I took photo reference, and I went back to start working. I think a lot about design quality when I'm making choices about placement. The tree and the staircase were design principals, a way of creating mystery through design. You can manipulate them to make them more interesting. I did that with the tree—made it whimsical. You wouldn't see something like that in nature.