I finished with this one, I think. Comments and critiques most welcome! Based (somewhat) on this photo https://flic.kr/p/aAVQDd
Very nice, I love the atmosphere! If I were to critique something myself, It would perhaps be the lack of vegetation (Ivy Gen), and maybe a some debris floating in the water. A few sun streaks here or there wouldn’t hurt. You could use something like an alpha mapped wood texture from CG Textures and shine your light through that (off-frame). Combined with a volumetric cube, It would help break the evenness up and add visual interest. Kinda what I mean: http://www.creativeshrimp.com/volumetric-lighting-blender-tutorial.html
Just a thought. If you did come back to this, post processing it to make it look like it was taken from an older camera would be cool. Could add a little “Lost Ark-esque” discovery feel. Still looks pretty nice in my opinion 
I like the overall simplicity, good job, however maybe adding something in the water causing some small waves would make the scene more interesting, or even a bird just touching the water…etc and also maybe you can decrease some parts of the displacement values of walls, to give more variety in the depth of displacement effect.
Yes, I like the simplicity as well, but you’re not the first one to point out that the scene is a little bit empty right now, so maybe i’ll try to add something for the eye to focus on. And the walls have no displacement, they’re pure geometry, I may give your idea a try though. Thanks for your comment.
Really great lighting and composition, but I agree that the water needs some work. I didn’t even notice it was a reflection at first glance.