This is beautiful subject matter, skillfully assembled into a photo. It works well as is, but for me there are a few distractions that keep it from fully coming together.
The main one is are the windows in the lower left. I like how they provide a counterpoint for all the round elements, but they may draw a bit too much attention away from the stairwell. They are much bluer than the top of the stairwell and I find myself drawn to them because of that. I also don't know if the small piece of the second window adds much to the composition.
A second, much less noticeable distraction is the red thing behind the railing in the lower right. It is probably a simple matter to clone that out. At least for me it doesn't add anything to the shot.
I think it may be possible to strengthen this already very appealing shot by eliminating the second window and balancing the blueness of the ceiling with that of the window.
Wow that is very cool.... you have really captured a very interesting angle of this staircase!! The colours you have have managed to keep a simplistic colour scheme and it has really helped you produce a good piece.