This is a nice take on Twilight's castle. And the fact that this has an observatory element reminds me a lot of Super Mario Galaxy. Although you've stated that you decided to give it a more dark and sinister theme, I could disagree, but on the same time, not really. The Moon shining in the indigo skies may invoke two different thoughts. One might say that it is dark and eerie, while the other could say that it is serene and that the Moon shining in the sky gives them hope.