Ancient giants have overrun the Copperbell Mines in Thanalan, and Momodi and Papashan ask you to deal with them.
How to Unlock
The Copperbell Mines, a 4-player dungeon, is unlocked by the level 17 Main Scenario Quest Into a Copper Hell.
Clear Shaft B4 of Rubble
Defeat the three enemies near the start of the dungeon and one of them will drop a tiny key. Interact with it to pick it up, then interact with the Sealed Blasting Door to use the key to unlock it.
All players need to stand in the elevator up ahead. (If you are using Duty Support, the NPCs do not need to stand in the elevator.) Once everyone is inside, a player needs to interact with the Lift Lever to move the elevator down to First Drop.
Up ahead, there is a room to the south that most players will want to skip. It does not contain any treasure coffers, so it is safe to skip it.
Farther ahead, a Hecatoncheir Stonehauler will burst out of the wall. A bit later, there is a path that splits off to the west, but it also does not have any treasure coffers, so it can be skipped.
Eventually you reach a dead end with a Powder Chamber, Blasting Device, and two bags of Firesand. Pick up both bags of Firesand (one of them is in the north end of this room), then interact with the Powder Chamber. (If you get an error message, look around this room for the other Firesand that you missed.) Then, interact with the Blasting Device to open the path.
Kottos will use Grand Slam, a high-damage attack on the player highest in the enmity list.
Lumbering Leap is a series of three large circle attacks, leaving only a small safe space.
Colossal Slam is a long cone attack.
Kottos sometimes targets a random player with Catapult, a single-target attack.
Clear Shaft E1 of Rubble
After you defeat Kottos, a Treasure Coffer and a Tiny Key will appear. Take the Tiny Key and use it on the nearby Sealed Blasting Door.
Up ahead, there is a treasure chest in a niche north of the elevator. As before, all players need to stand in the elevator. (If you are using Duty Support, the NPCs do not need to stand in the elevator.) Once everyone is inside, a player needs to interact with the Lift Lever to move the elevator down to B2.
There is another Powder Chamber and Blasting Device up ahead. To get the Firesand for it, you need to defeat the enemies in the west and east rooms off to the side. The eastern room also has a treasure chest to the south. The Blasting Caps in these areas will each drop Firesand when killed. Be sure to pick up both pinches of Firesand.
Afterward, interact with the Powder Chamber to put the Firesand in (if you get an error message, be sure to kill all nearby enemies and pick up all Firesand that they drop), then interact with the Blasting Device to open the way.
Up ahead, be sure to pick up the Firesand. Then, you will encounter a large green blob called Ichorous Ire.
Ichorous Ire sometimes a random player with Syrup, a small circle attack.
It sometimes targets the player highest on the enmity list with Fluid Spread, a high-damage attack.
When it casts Divide, it generates untargetable Ichorous Drips around the room, which each cast Burst, a circle attack centered on each one. Move to a safe area to avoid getting hit.
Arrive in Shaft E2
Afterward, pick up the Firesand that appeared, then interact with the nearby Powder Chamber (if you get an error message, backtrack a short distance to find the other Firesand), then use the Blasting Device.
Defeat Gyges the Great
Fight your way through the next area. There is an optional treasure chest in the southern part of the area. Then go toward the northwest, where a Hecatoncheir Stonebreaker will burst out of the wall. Then go farther northwest to reach the dungeon boss.
Gyges the Great
Gigantic Swing is a large donut attack, where the only safe spot is under the boss. Quickly move under the boss to avoid the attack.
Gigantic Smash is a circle attack centered on the boss, which is also accompanied by circle attacks around the room a moment later. Move away from the boss, then move out from any additional circle attack markers that appear.
Grand Slam is a high-damage attack on the player highest on the enmity list.
Colossal Slam is a cone attack aimed at a random player.
Completing the Quest
Defeating Gyges will complete one of the quest objectives for the Main Scenario Quest Into a Copper Hell.