Very cool castle. Like the architecture and the colors you chose to tone it. The blown-out clouds in the background are a bit distracting, but, other than go to take the photo at some other time, there's not much you can do about that in a basic editing challenge. :)
The processing is fairly noticable. However, the castle itself is pleasing so the soft halos that are seen do not detract in general. The sky however isn't as pleasing, IMO. It's very harsh and it doesn't compliment the castle very well which has softer tones to it. I do like how there is a break in the clouds so the background isn't all white.
In regards to the rest, the duotone looks good. I also like the composition and you've managed to produce a lot of detail in the shadows despite the harsh light. Good photo.