Open Locked Vault Doors in Dungeons:
At the end of some Dungeons there will be locked vault doors that when unlocked will lead to secret endgame dungeons that have higher level enemies and better rewards. There are 8 locked vaults in total that lead to endgame raids and they are listed as follows:
Keycatrich - Level 55
Grotto - Level 65
Fociaugh - Level 65
Daurell - Level 72
Balouve - Level 78
Steyliff - Level 86
Crestholm - Level 92
Costlemark - Level 99
These endgame raids are only accessible after finishing the story.
Before sprinting turn on the Stamina Bar at the 'Pause' screen. When you sprint the stamina will deplete but if you let go of the sprint button just before the Stamina Bar depletes (within 0,6 seconds before it depletes) Noctis will glow green and the stamina bar will instantly refill. If you keep doing this you will be able to sprint continually.