Incredible, really love the cluster shapes and subtle dithers. The pallet is really nice, great concept and the composition looks very dynamic and intersting.
Good job all around :>
I know, I know, it was just a silly Monty Python reference. I can see the pieces of rock and dirt falling down on the huge tracts of land as the islands float up, it's very nice. 
Thanks, CELS! The islands are actually going up, the castle wasn't made by a daft hahaha
Thanks, Hapiel! I didn't use a reference for the rocks, I just made some diamond shapes with shadows below
"Everyone said I was daft to build a castle on a floating island but I built it all the same, just to show 'em." Nice pixelling, cool take on this idea! Really making the viewer curious. Would have been nice to see some more shadows (or even hints of god rays / backlighting) 
Cool piece, that must have been a lot of work! It's an interesting rock structure, what inspired you to make it like that?
This is great.