Warning! Mild spoilers ahead.
In the opening sequence of Star Wars: The Rise of Skywalker, Kylo Ren and his Stormtroopers fight mysterious enemies in a forest environment. After the battle, Kylo seizes the Wayfinder and leaves the planet.
You may be surprized to learn that this sequence takes place on Mustafar, the volcanic planet where Anakin Skywalker and Obi-Wan Kenobi fought in Revenge of the Sith. This information comes from the official Visual Dictionary of The Rise of Skywalker.
According to this book, the appearance of Mustafar is now different because patches of the surface have started to cool within the last decades. These events are told in the Vader Immortal VR games.
Kylo finds the Wayfinder in the last remnants of Darth Vader’s castle, which appeared in Rogue One. His enemies are “cult colonists” who worship Vader.