Sepulcher of the first ones
The Sepulcher of the First Ones is a First Ones-style structure overlooking Zereth Mortis from a secluded island on the eastern end of the zone. Initially, you will need to use an Ancient Translocator located east of Pilgrim's Grace to get to the raid which is unlocked at the end of Chapter 4 of the Patch 9.2 questline, Forging a New Path.
The raid entrance is located on a floating isle in Zereth Mortis. First, you must fly to Pilgrim's Grace. Upon arriving there, climb up a set of stairs to your left, interact with the Ancient Translocator to fly to the Sepulcher raid.
After flying is unlocked in Zereth Mortis, you can simply fly to the raid entrance.
Ilevel requirements follow similar trends to previous raids of the expansion, where the majority of the bosses have a specific set ilevel for loot they drop, with the final three being higher (and thus, will no doubt require a higher ilevel to defeat).
LFR will drop Item Level 239 gear for the majority of the bosses, rising to 246 for the last three, with a 220+ ilevel entry requirement.
Normal will drop Item Level 252 gear for the majority of the bosses, rising to 259 for the last three, with a 239+ ilevel entry requirement.
Heroic will drop Item Level 265 gear for the majority of the bosses, rising to 272 for the last three, with a 252+ ilevel entry requirement.
Mythic will drop Item Level 278 gear for the majority of the bosses, rising to 285 for the last three, with a 265+ ilevel entry requirement.
Sepulcher of the First Ones Boss Order
Sepulcher has a semi-linear boss order, with a few points where you need to defeat all available bosses before being allowed to continue.
The Jailer has breached the Sepulcher, the mysterious heart of the Shadowlands. Should he control its primordial power, he will reshape the cosmos with Death at the fore. As Zovaal prepares to dominate reality, champions of Azeroth charge forth to stop him. Will their resolve outmatch his?