I can't quite place it...The sky & terrains are fantastic, atmosphere is perfect. Something about the main focus...the tower/beacon has a subtle structure yet it's terrain base does not match the rest of the terrains which are sharp & craggy. maybe roughen that surface a bit or give the tower some kind of extended supports like fins or legs.(more ominus?) does that make any sense? Just thinking out loud. my .02

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Ockham's razor- It's that simple