There are locked vault doors at the end of some dungeons that lead to secret raids when unlocked. First, complete the story by completing all 14 chapters. After the credits, create a save game. Load the saved game, go to a lodging, and call Umbra to travel back to any of the locations in the game. Then, complete the following four dungeons: Balouve Mines, Crestholm Channels, Daurell Caverns, and Costlemark Tower. Next, go to the Meldacio Hunter HQ outpost in the very north of Cleigne. There is an old lady sitting in a chair. If you have completed the previous steps, she will be marked as a quest giver. Talk to her to get a key for all dungeon vaults. She will also give you several "Menace" quests. Track a Menace quest for it to add a waypoint to the next vault on the map. Behind those doors are deeper levels of the dungeons with higher level enemies and better rewards. These endgame raids are only accessible after completing the story. It is recommended to go to them well prepared, as they have the strongest enemies in the game and take a very long time to complete. If you want the very best equipment in the game, this is where to obtain it. There are eight sealed vaults that lead to raids:

Balouve - Level 78
Costlemark - Level 99
Crestholm - Level 92
Daurell - Level 72
Fociaugh - Level 65
Grotto - Level 65
Keycatrich - Level 55
Steyliff - Level 86