idir_hh said:

I think I might have found the perfect spot to sneak in Vader’s castle!

You can literally grab the silhouette of Vader’s castle from the deleted scene here:
https://i.redd.it/gcrk2oz4zr451.jpg

And mask it into the the background of this shot here:
https://pbs.twimg.com/media/EVHT9DpU8AAVtHG.jpg

idir_hh said:

Hal 9000 said:

Oh yeah, and if anyone so inclined wishes to add a distant Vader’s castle to the reverse shot when Kylo picks up and looks at the Wayfinder, I won’t try to stop you.

One can mask this landscape into the background of that shot:
https://i.pinimg.com/originals/75/c1/1b/75c11b8ae85a1c727c5b20b081beff2a.jpg

Showing that Kylo Ren’s slaughter happened below Vader’s Castle, perhaps even where Anakin fell at the hands of Obiwan.