You enter the Stone Vigil, a keep overrun by Dravanians, to search for the missing airship, Enterprise.
How to Unlock
The Stone Vigil dungeon is unlocked by the level 41 Main Scenario Quest In Pursuit of the Past.
Secure the Barbican
Go north up the hallway, then turn right and make your way around the hall. Koshchei will descend from above and breathe fire down the hall, damaging anyone in its path. You can go into one of the rooms on the right to avoid this.
At the dead end, go west into the large room and go southwest through it to the western hallway. Go north and make your way around the hallway. When you reach the hallway to the north, Koshchei will again descend from above and breathe fire down the hall.
Go north through the hallway and you will find Chudo-Yudo.
The tank should turn Chudo-Yudo to face away from the rest of the party.
Chudo-Yudo periodially casts The Lion's Breath, a cone attack that inflicts burns on those it hits. The healer can use Esuna to remove this.
After a while, Chudo-Yudo will go to one side of the room and cast Swinge, a very large cone attack. Quickly get behind or to the side of Chudo-Yudo to avoid this attack. It will inflict Pacification and Silence on those it hits.
Retake the Right Brattice
After you go north from Chudo-Yudo's room, you can optionally go to the right to get a treasure coffer.
Go west, and when you reach the end of the hallway, Koshchei will descend again to breathe fire down the hall. Go north to a larger area. When you go east from there, Koshchei will descend and breathe fire again. Go farther east, then north up the hall. When you reach the window in the middle of this hallway, three Ice Sprites will appear. You can optionally go into the room on the left to get a Treasure Coffer.
Go north from there, and eventually you see flames blocking your path. Go east from there and you will find Koshchei, the dragon who has been breathing fire down the hallways.
Spiked Tail is a high-damage attack on the player highest in the enmity list.
Sonic Storm targets a random player with a circle attack marker.
Typhoon makes whirlwinds appear along the east edge of the area. The first time this attack is used, there will only be three whirlwinds. The whirlwinds will move westward across the area. Don't stand in the path of any of the whirlwinds or you will take damage and be thrown into the air. Note that two of the whirlwinds move first, and the third moves later.
From then on, when the boss casts Typhoon, there will be four whirlwinds. As before, two whirlwinds will start moving first. Stay out of the path of these first whirlwinds to move, then when they have gone past, walk behind one of them so that you will not be hit when the second set of whirlwinds begins to move.
Go west, then north up the passage that was previously blocked by flames. When you reach the long hallway to the north, three Ice Sprites will appear at the first window. There is an optional room on the left where you can get another treasure coffer.
Go north from there, and three more Ice Sprites will come in from the second window. Continue going north and you will reach the Strongroom Gate. Open it and go north into the final boss's room.
The tank should turn Isgebind to face away from the rest of the party.
Isgebind will sometimes cast Frost Breath, a cone attack.
It will also sometimes target a random player with Sheet of Ice, a circle attack. If you don't get out of the attack marker in time, you will be inflicted with Paralysis. This attack places a temporary ice puddle on the floor. Players who stand in these puddles will get a Frostbite debuff. Step out of the puddle to remove this debuff.
After taking a certain amount of damage, Isgebind will fly upward, then will start casting Cauterize, which will mark a large part of the floor with a large ice line attack that Isgebind will swoop past, breathing ice. Getting hit with this will inflict a Frostbite debuff.
After these ice line attacks, Isgebind will land on the ground and use the Touchdown attack, knocking back all nearby players and inflicting damage.
Later in the fight, Isgebind will sometimes use Rime Wreath, which does damage to all players.
Completing the Quest
Defeating Isgebind will complete one of the quest objectives for the Main Scenario Quest In Pursuit of the Past.