The first few minutes of Star Wars: The Rise of Skywalker stealthily snuck us onto a planet we’ve visited before in the Star Wars saga. A planet integral to the prequels, in fact.
As noted by EW, Pablo Hidalgo’s Star Wars: The Rise of Skywalker: The Visual Dictionary actually names the first planet we’re on, as we watch Kylo Ren hack, slash, and rock bottom his way through enemies.
It’s Mustafar, the planet from Episode III: Revenge of the Sith where Obi-Wan and Anakin clashed among volatile pools of lava. Mustafar was also briefly featured in Rogue One: A Star Wars story since it’s where Anakin, as Darth Vader, built his menacing lair. Which is the exact castle Kylo is trying to infiltrate at the beginning of Rise of Skywalker.
Source: IGN.com This Classic Star Wars Planet Was Actually in Rise of Skywalker