Author's Note: Well, first of all, this is not a castle or a castle's tower, it is a tower surrounded by walls.
Alright so, the sand symbolizes the bright shining Sun, the moss stone symbolizes the Moon, and lastly, the trees on the highest point symbolizes Life on Earth.
So... yeah, felt like making it. Totally made out of sand, mossy cobblestone and stone steps, no sandstone what so ever.
Also, used MrMessiah's BetterLight mod and the BroPaint Texture Pack.