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

A Sith cave was located on the Outer Rim planet Mustafar, a volcanic world known to house a locus for the dark side of the Force deep beneath its surface. 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 this energy to "bleed" a kyber crystal in order to construct his own lightsaber. Later, a castle was built over the ancient structure, which was designed to channel the dark side of the Force and to serve as the personal residence of Darth Vader.

Description
The ancient Sith cave was located on the volcanic planet of Mustafar, an Outer Rim world known to house a locus for the dark side of the Force deep beneath its surface. The cave resided in the course of a lava river&mdash;the incoming lava left the cave as a lava fall, dropping from the other side of the cave. The interior of the Sith cave featured various markings on its walls, as well as a round table at the center.

History
"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

By order of his master Darth Sidious, the newly-christened Sith Lord Darth Vader traveled to Mustafar, where he lost his remaining limbs and suffered severe burns all over his body as a result of his duel against his old Jedi master Obi-Wan Kenobi, after he successfully stole a Jedi's lightsaber in the year 19 BBY. To construct a lightsaber of his own, Vader needed to draw upon the cave's dark energy and "bleed" the seized saber's kyber crystal&mdash;corrupting the crystal with the power of the dark side, turning its color to red during the process. After he placed the green-colored crystal on the table inside the cave, the markings on the walls started 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 got out of the vision and finally bled the kyber crystal.

By 5 BBY, Vader had constructed his own castle over the Sith cave, which was also once a site of an ancient castle full of dark secrets. The massive obsidian tower was designed to channel 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, an art book for Rogue One released on December 16, 2016, the same day as the film itself. The Sith cave made its first canonical appearance in Darth Vader: Dark Lord of the Sith 5: The Chosen One, Part V, a comic book written by Charles Soule with art by Giuseppe Camuncoli, and released by Marvel Comics on September 6, 2017.

According to Doug Chiang, co-production designer for Rogue One, the idea of a Sith cave beneath Darth Vader's castle originated from a concept art for the Emperor Palpatine's throne room featured in Episode VI Return of the Jedi. The concept art was designed by Ralph McQuarrie, the legendary conceptual designer responsible for many of the designs and aesthetics featured in the original trilogy. Chiang found this image of the throne on a lava lake inside a cave compelling, and decided that the castle would be built on a foundation of an ancient structure. He intented to give the final design of the castle an element of a structure that was there for a purpose, which was to draw energy from the lava lake like a lava lake dam. Furthermore, he thought that maybe even deeper there could be an even more ancient part, which was a natural cave where Vader went to meditate.

Although the StarWars.com Databank entries for "Darth Vader" and "Mustafar" explicitly state 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." Though at first glance this may be viewed as a minor continuity error, the Lucasfilm Story Group's Pablo Hidalgo, the book's writer, clarified that "it depends how deep you dig," thus the two sources do not contradict.

Appearances

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