This is a truly stunning work of art. From the first glance at the thumbnail, you know that it's going to be real pretty when you click on it to see details. What is admirable is that this image 'works' in all dimensions - thumb, small and full view. The imperfections - all very tiny and not annoying - are visible only after analysing the big version.

On the technical side, the first bad thing I noticed is the sky. Stock photo(s) used for it were rather grainy and it shows. It causes a dissonance with very good quality of the bottom half of the image. The only other thing (which I noticed only after reading the comments) is the little statue at the top of the building. Its color is a bit different than the palette of surrounding rocks and it seems to be blueish in comparison. Once you know it's there, you keep noticing it all the time.

The image has a couple of quirks that give this image unrealistic, fantasy feel. First, it's lighting. It's obviously sunset, but the foreground is very light, as if glowing on its own volition or being lighted from the front. The tree, the dips of terrain, the rock formation - they all cast very little shadow. The colors are very vibrant, especially the weird orange grass in the foreground. Pink hues of the sky form a halo of sorts around the building - subtle thing, but very meaningful.
The second issue is the unnatural sharpness. The viewer can see every detail, regardless of the distance. You can see even separate strands of grass and cracks in the rocks!
It all induces an unsettling feeling; at first glance, the landscape is very realistic, but then you start to notice all these weird things and begin to wonder. This image plays tricks with the viewer; it's hard to look at it for longer time and not start to get a sinking feeling that something is wrong with it. I personally think that this unnatural aspect of this landscape is brilliant (benefit of the doubt), but it can be counted as a flaw/error on artist's part.

In my opinion, this image is rather original when it comes to photomanipulation category. It's rare to see a building so immersed into elements of nature in a photomanip. I am left to wonder why it was built in such a location - lonely slab of rock in the middle of nowhere, where was the entrance (in the deep shadows lurking in the crevices?), why the tree next to it died while the one in the distance is still full of life. The crows (are they crows?) add to the unsettling atmosphere of this place.

All this, paired with very rich color palette, create a very good, seamless photomanip that's hard to forget. I wish there were more such images in photomanipulation category.