Now that you have the key, you can try to find the underwater tunnel to enter Ala Mhigo.

Requirements

This quest is available if you have completed the quest The Key to Victory.

Starting the Quest

Talk to Lyse in The Lochs to begin the quest.

Follow Lyse

Go northwest to exit the building, then go north and through the archway in the wall. From there, go northeast to where the orange arrow is pointing in the minimap. Talk to Lyse and there will be a cutscene.

Speak with Lyse in Loch Seld

Go north and swim in the water, then dive underwater by pressing Ctrl+Spacebar on keyboard or by pressing B on Gamepad. If it doesn't work, swim farther away from the edge of the loch and try again.

Once you are underwater, swim downward and face the direction of the quest icon on the map, and you will see a tunnel surrounded by glowing crystalline forms. Swim into that tunnel and talk to Lyse.

Follow Lyse Again

Swim into the tunnel and when you can't go farther forward, go upward in the small opening where light is shining down. In the room where you emerge, go up the stairs and follow the path until you find Thancred and Lyse. Talk to Lyse to proceed.

Speak with Lyse

There will be a glow around Lyse, indicating an instanced battle. Check on her and the battle will ensue.

Solo Duty: The Resonant

Approach Thancred and follow him when he starts moving. Follow Lyse behind the wall when Thancred says to take cover, then follow Thancred when he moves again.

Go to the right side of the large gate to find the Gate Winch. Check on it.

Afterward, follow Thancred, and you will be attacked by several groups of enemies. Defeat the Hoplomachus that is focusing on you, then defeat the other enemies. Follow Thancred again, then defeat the Magitek Reaper that is focusing on you, then defeat the other enemies. Follow Thancred once more, then defeat the Magitek Predator that is focusing on you, then defeat the other enemies. Follow Thancred again, and there will be a cutscene.

Defeat Fordola

Whenever Fordola is casting Resonant Echo, wait for the spell to complete. This will give her Resonant status. At that point, use the Aetheric Siphon to inflict Aetheric Sickness on her.

Avoid standing in the Chopping Block circle attack markers.

Get out of the way of the laser line markers on the ground from the Magitek Bits.

Whenever Fordola goes to the center and casts Terminus Est, creating four glowing Xs, make sure that you are not standing in front of where any of the Xs are facing when she finishes casting The Order, which makes the Xs do a line attack in the direction that they are facing.

After the battle, there will be a cutscene. This one is important, so it is recommended to watch it either now or via the Unending Journey in an inn room.

Speak with Alphinaud

Talk to Alphinaud to complete the quest.

Next Main Scenario Quest

After you complete the quest, talk to Alphinaud to accept the next quest: The Legacy of Our Fathers.