Sith cave

"Mustafar is not like other planets. It is unique. Deep beneath its surface rests a locus for the dark side of the Force."

- Darth Sidious

An ancient Sith cave located deep beneath the surface of the volcanic Outer Rim planet Mustafar served as a locus for the dark side of the Force. The cave resided in the course of one of the planet's lava rivers and was strong with dark-side energy.

Shortly after the rise of the Galactic Empire, the newly-christened Sith Lord Darth Vader traveled to the Sith cave to use its energy to "bleed" a kyber crystal in the construction of his own lightsaber. Vader later built a castle over the cave to channel the power of the dark side and serve as his personal residence.

Description
"When you arrive on Mustafar, find the place where the dark side calls to you. Draw upon the energy there&mdash;combine its power with your own. Then&hellip; use it."

- Darth Sidious, to Darth Vader

An ancient Sith cave was located on the volcanic Outer Rim Territories planet Mustafar and served as a locus for the dark side of the Force. Situated deep beneath Mustafar's fiery surface, the cave resided in the course of a river of lava, which flowed through and dropped out of the cave as a lava fall. The cave's interior featured various markings on its walls, as well as a round rock table naturally formed at its center.

Bleeding the kyber crystal
"Here, you will reclaim yourself. From the site of your greatest defeat, you shall rise&mdash;strong, unbroken&hellip; powerful."

- Darth Sidious, to Darth Vader

Shortly after the formation of the Galactic Empire in the year 19 BBY, the Sith Lord Darth Sidious ordered his newly-christened apprentice, Darth Vader, to steal a Jedi's lightsaber in order to construct one of his own. After obtaining Jedi Master Kirak Infil'a's lightsaber, Vader, again following his Master's orders, traveled to Mustafar, where he had previously suffered severe burns all over his body as a result of his lightsaber duel against his old Jedi Master, Obi-Wan Kenobi.

To complete the task of constructing his new lightsaber, Vader needed to draw upon the Sith cave's dark energy and "bleed" the stolen lightsaber's green kyber crystal&mdash;corrupting the crystal with the power of the dark side and turning its color to red in the process. After Vader placed the crystal on the cave's rock table, the markings on the walls began to glow as he experienced a Force vision in which he denounced the dark side, killed Darth Sidious, and returned to Kenobi's side. By re-embracing the darkness, Vader escaped the vision and finally bled the kyber crystal.

Building Darth Vader's castle
"You sent me to Mustafar to bleed my kyber crystal at the dark side locus present on the planet. When I touched that power, I saw deeper into the Force that ever before. I believe things are possible at the locus that are impossible elsewhere."

- Darth Vader, to Darth Sidious

Impressed by the Sith cave's dark power and the possibilities that came with it, Vader later decided to build a castle over the dark side locus and make Mustafar his stronghold. The Sith Lord's request was approved by Sidious, who speculated that Vader would perhaps be able to resurrect his deceased wife Padmé Amidala by using the dark-side energy there. The Sith Master also told his apprentice to take the mask of Lord Momin&mdash;a Sith artifact that once belonged to the ancient Sith sculptor Momin, who went against the Sith's legacy of destruction and instead preferred to create&mdash;with him as it could prove useful for Vader's quest.

Vader traveled to Mustafar aboard his late wife's royal starship and was accompanied by Imperial architect Alva Brenne along with her assistant Roggo. While Vader was meditating alone inside the cave, Roggo became possessed by Lord Momin's mask and killed Brenne. Vader soon returned to the starship parked near the cave's entrance, and found Roggo working on the fortress' design while wearing the ancient mask. The Sith then killed the possessed Imperial with his lightsaber and retrieved the hologram of the design, which looked close to the castle's final form.

Vader's fortress that stood atop the Sith cave, which was also once the site of an ancient castle full of dark secrets, was completed by 5 BBY. The massive obsidian tower was designed to channel the power of the dark side of the Force&mdash;it was divided in the middle to resemble tuning forks and harnessed Mustafar lava for energy.

Behind the scenes
"We don't see it all right now, but the idea was that Vader's castle was built over a natural cave&mdash;a Sith cave deep down below, in the lava world."

- Doug Chiang

The Sith cave was created as part of the backstory for Darth Vader's castle, which was designed for Rogue One: A Star Wars Story, the first film in the Star Wars Anthology Series. The cave was first mentioned in The Art of Rogue One: A Star Wars Story, published on December 16, 2016, the same day as the film itself. The Sith cave made its first canonical appearance in the comic book Darth Vader: Dark Lord of the Sith 5: The Chosen One, Part V, written by Charles Soule with art by Giuseppe Camuncoli, and released by Marvel Comics on September 6, 2017. The ongoing story arc Fortress Vader of the Star Wars: Darth Vader: Dark Lord of the Sith comic book series further explores the creation of Vader's castle.

According to Doug Chiang, co-production designer for Rogue One, the idea of a Sith cave beneath Darth Vader's castle originated from a piece of Ralph McQuarrie concept art of Emperor Palpatine's throne room created for Star Wars: Episode VI Return of the Jedi. Chiang found the image of the throne on a lava lake inside a cave compelling and decided that the castle would be built on the foundation of an ancient structure. He intended to give the castle's final design an element of purpose, which was to draw energy from the lava lake much like a dam. Furthermore, Chiang thought that the castle could have a more ancient part below it, in the form of a natural cave where Vader went to meditate.

Although the StarWars.com Databank entry for "Darth Vader" explicitly states that Darth Vader's castle was built over an "ancient Sith cave," the 2016 reference book Star Wars: Rogue One: The Ultimate Visual Guide states that it was built over an "ancient castle full of dark secrets." Although this is an ostensible continuity inconsistency, the Lucasfilm Story Group's Pablo Hidalgo, the book's author, clarified that "it depends how deep you dig." Additionally, the 2017 reference book Star Wars: Absolutely Everything You Need to Know, Updated and Expanded also supports the aforementioned book's statement.

Appearances

 * Darth Vader: Dark Lord of the Sith 5: The Chosen One, Part V
 * Darth Vader: Dark Lord of the Sith 21: Fortress Vader, Part III