The cascading pink flowers need more texture. Right now they look like single brush strokes. Otherwise, this is just about perfect. I don't see any other obvious signs that it's a manipulation rather than an actual photo. Great job!
Cool! I love the blurry leaves in the front to give the picture some context. I like how the garden grows fronds into the fountain. I like the observatory/building up top - I would totally live there. And the view is amazing! Very well done.