Benusta:
Krofin's Nest is inhabited by ancient monsters - Krofines. They were considered to be eliminated by Giants, but unfortunately that is far from truth. Krofines are under command of their queen, Krosha. They won't be as dangerous without her, so you need to go to Krosha's layer and destroy her. You need to select the difficulty after entering the zone. Regardless of the selected difficulty and your results you cannot re-enter the Krofin's Nest 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.