At first I couldn't tell where Roland had ended up, since the towers in the background are certainly not the Dark Tower! I'd guess somewhere along the fringes of the Mohaine desert, the apotheosis of all deserts....
The detail on Roland is fabulous, especially his upper coat. The background itself is fine, but the structures, especially the near/foreground tree, could've done with a bit more clarity. I don't recall reading about a tilting spire like the one on the left... where has Roland gone, I wonder ;)