Benusta:
Defeat all monsters in Nightmare Kamaloka.
You need to select the difficulty after entering the zone. Regardless of the selected difficulty and your results you cannot re-enter the Nightmare Kamaloka instance zone until the access limit resets at 06:30.
Keep in mind that you can reenter the zone during the battle, however if all the party members leave the zone, they should re-enter it within 1 min.