Rogue One will have to settle for being the second-highest grossing film of the year — damn you, cultural juggernaut Finding Dory! — but it does have the distinction of being among the better-reviewed films in its franchise. Many critics have praised director Gareth Edwards’ vision of some unexplored pockets of George Lucas’ universe, singling out Darth Vader’s castle lair that appears in the film on a violent, molten-lava planet. (The planet bears a strong resemblance to Mustafar, the magma-covered site of the final showdown between Anakin Skywalker and Obi-wan Kenobi in Revenge of the Sith.) Now, one of the key designers from Rogue One has provided a little background on the memorable locale and how it came to be.