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 on the Gahenn plains, and was strong with dark side energies.

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 decided to build a castle over the cave that could channel the power of the dark side in order to resurrect his deceased wife, Padmé Amidala, which would ultimately prove futile. Using the designs came from the ancient Sith Lord Momin through his spirit preserved within an artifact, Vader constructed a massive obsidian castle that would 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 Gahenn plains on the volcanic Outer Rim Territories planet of 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 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

The Sith cave resided in an area that was once the site of an ancient castle full of dark secrets, and a Sith temple. 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.

Return to Mustafar
"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 his own fortress 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 energies there. The Sith Master also told his apprentice to take the Mask of Lord Momin&mdash;a Sith artifact that possessed the spirit of the ancient Sith sculptor Momin, who went against the Sith's legacy of destruction and instead preferred to create artworks that would evoke pain and fear in viewers&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 Chief Imperial Architect Alva Brenne along with her assistant Roggo. While Vader was meditating alone inside the cave, Roggo became possessed by 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 early design. Vader subsequently took the mask with him inside the cave, and used the Force to activate it. The mask's eyes glowed red, as Momin's spirit began telling Vader his story&mdash;his sculpting philosophy that he adopted as a youngling, how he was trained in the ways of the dark side by Sith Lady Shaa, and his ultimate defeat by the Jedi before he could complete his "masterpiece."

When the mask finished his story to Vader, the Sith Lord realized that he had removed his helmet and was wearing Momin's mask instead. Taking off the mask immediately, Vader left the cave, attacked a nearby Mustafarian patrol, and captured a Northern Mustafarian named Sssp. By forcing the captive to wear the mask, he allowed Momin to possess the native's body.

Designs of Lord Momin
"The door to the dark side is locked. This is the key. Your beloved waits for you there, Vader. Beyond the door. My fortress will tune the energies of the locus. It is your first step toward using the power of the dark side to pierce the veil of time, between life and death."

- The Mask of Lord Momin talks to Darth Vader about his fortress design

Vader and the possessed Mustafarian soon returned to the Sith cave as the Dark Lord asked Momin about the design he made while corrupting Roggo's body. The Sith sculptor claimed that his design would be the key to unlock the locus's dark power capable of resurrecting Vader's beloved and breaking the boundary between life and death. Stating that he had been lied about the dark side's ability to prevent death before, Vader warned Momin not to deceive him while choking him with the Force. Momin, however, asserted his claim and told Vader that he would use the opportunity Vader provided to him to finally make his "masterpiece."

An Imperial construction site was soon established around the Sith cave, which was protected by stormtroopers, AT-ACT and AT-ST walkers, along with TIE fighters, against lava flea–riding Mustafarians attacking the site. After eight failed designs, with each causing powerful lightning storms and lava overflows across the planet that resulted in the construction's destruction, the castle was finally completed by 5 BBY. In the final design, several rectangular, inclined objects were placed around the table at the center of the cave, which served as the focusing chamber for the dark side energies. The massive obsidian tower was designed to channel the power of the dark side&mdash;it was divided in the middle to resemble tuning forks and harnessed Mustafar lava for energy.

A portal through the Force
"This new design for the focusing chamber&hellip; It just feels right, doesn't it, Lord Vader?''" "''Yes. The power here&hellip; This was its destiny. This is what it was waiting for."

- The Mask of Lord Momin and Darth Vader

By using the Force while positioned in front of the table inside the cave, Vader activated the castle as a burst of light in various shapes shot from the top of the tower and up through the sky. Although he successfully opened a portal through the Force, Vader's efford was interrupted by Captain Junus, commander of the castle's Imperial garrison who reported to the Sith Lord that they were under assault by a large army of Mustafarians. When Vader left the cave to inquire about the situation, Momin activated the castle and used its power to provoke a lightning strike on Vader outside. He soon opened the portal for himself and summoned his physical body. The newborn Momin took his mask back from the body he formerly used as a host, and proclaimed that he himself was his "masterpiece."

Upon noticing that Vader had joined the battle, Father Kkkt and two other Force-sensitive Mustafarians combined their strength to flood the battlefield with lava, killing both Imperial and Mustafarian combatants alike. As the sole Imperial survivor, Vader retreated to the castle while the remaining natives launched their final attack to destroy the dark fortress. Back inside the Sith cave, the Dark Lord activated the castle in order to erupt the lava in the area surrounding the fortress, and decimated the rest of the Mustafarian army.

Momin subsequently revealed his resurrection to Vader, and the two Sith engaged in a lightsaber duel inside the cave. Although Momin seemingly had the upper hand after cutting Vader's lightsaber-holding hand as he claimed the dark side would never allow Vader to reach the other side of the portal, Vader eventually overpowered and killed Momin by smashing him to the wall with one of the rectangular objects around the table. Having defeated all his enemies, Vader finally reopened the portal to resurrect Amidala.

While the Sith Lord's body left unconscious inside the cave, Vader's soul passed through the gateway. Afterward, Vader faced various figures and events from his past, also experienced brief visions of the future such as his confrontation with his former Jedi Padawan, Ahsoka Tano, at the Sith temple on Malachor. He eventually reached a seemingly alive version of his wife, although he ultimately couldn't manage to save her as she rejected him, stating that Anakin Skywalker whom she knew was dead. Vader's vision was soon broken with the appearance of a distant figure wielding a blue lightsaber, which was actually Vader's son&mdash;Luke Skywalker&mdash;unbeknownst to him. As the Dark Lord's body regained his consciousness, he destroyed the gateway by stabbing the rock table with his lightsaber, and accepted his fate. The portal's destruction caused the lower ground in front of the castle to collapse, revealing other buried structures.

Backstory for Vader's castle
"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 final story arc Fortress Vader of the Star Wars: Darth Vader: Dark Lord of the Sith comic-book series further explored 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.

Continuity issues
"Let's just say it depends how deep you dig. And there's more to come."

- Pablo Hidalgo

Although the StarWars.com Databank entry for "Darth Vader" explicitly states that Vader's castle was built over an "ancient Sith cave," with Star Wars: Darth Vader: Dark Lord of the Sith comic-book series later depicting the actual construction, 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.

The 2017 Star Wars: The Last Jedi: The Visual Dictionary establishes that Supreme Leader Snoke's ring featured obsidian from catacombs beneath Vader's castle, while the 2018 Star Wars: The Complete Visual Dictionary, New Edition mentions that Vader's castle was once the site of a Sith temple. When asked if the former actually refers to the Sith cave, the Lucasfilm Story Group's Matt Martin stated that was "a bigger question for another time." The twenty-fifth and final issue of Star Wars: Darth Vader: Dark Lord of the Sith comic-book series later revealed buried structures beneath the castle other than the Sith cave.

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
 * Darth Vader: Dark Lord of the Sith 22: Fortress Vader, Part IV
 * Darth Vader: Dark Lord of the Sith 23: Fortress Vader, Part V
 * Darth Vader: Dark Lord of the Sith 24: Fortress Vader, Part VI
 * Darth Vader: Dark Lord of the Sith 25: Fortress Vader, Part VII