We finally got to see where Darth Vader hangs his cape and calls home in Rogue One: A Star Wars Story. This was a really cool scene in which we are shown the dark and sinister castle on the hot and fiery planet of Mustafar.
Vader was ordered to live there by The Emperor as a constant reminder of his anger at Obi-Wan Kenobi and what he did to him. Remember, that’s the place where Obi-Wan sliced all his limbs off with his lightsaber and left him being burned to a crisp.
“Dark Monolith: Vader’s personal abode is an obsidian tower on an inhospitable world. It is the Emperor’s design that Vader lives in such an unforgiving environment. Vader’s attendant, Vanee, visits Vader as he meditates within a rejuvenation chamber. The stark, modern structure is built over an ancient castle full of dark secrets.”
There’s also more information In the Art of Rogue One book from production designer Doug Chiang, who reveals the following:
“We don’t see it all right now, but the idea was that Vader’s castle was built over a natural cave — a Sith cave deep down below, in the lava world.”
I would love to see all this ancient Sith stuff deeply explored in the Star Wars universe some day in the franchise and it sounds like that’s going to happen. Chiang goes on to say that they brought the castle into the picture with the idea of exploring it in future Star Wars projects that are canon.
“Vader’s Mustafar castle in Rogue One would be concepted, designed, and explored beyond even the narrative needs of Rogue One itself. We were building worlds, so we always had to keep in mind the broad strokes and the big picture, in case they were needed for the story.”
The castle was originally designed by concept artist Ralph McQuarrie for George Lucas. Lucas was toying with the idea of using it in The Empire Strikes Back, but he obviously never went through with it. You can see the art that he created for it above.