How to Unlock The Aitiascope

Arrive at the central observatory: You'll start in the first room. Take out the two enemies there to get past the first wall. In the next room, you'll find a pack of five enemies. Pull them towards the next wall, and then grab another three enemies. Watch out for a large AoE attack from a Sinking Rivalry in this area. The final room here pits you against Ilberd the Unrelenting. He'll spawn more enemies, but you only need to lower their HP a bit – they'll be instantly killed.

Clear the central observatory: Your next task is to defeat Livia the Undeterred. Once she's down, you'll get a Treasure Coffer.

Arrive at the saltcrystal strings: At the start of this new area, you'll find a pack of three enemies, followed by two more before you reach a wall. Keep an eye out for a yellow spirit; it uses a friendly AoE, so lure the enemies towards it. Make sure to open the Treasure Coffer here. Then, head to the next yellow spirit and wait for it to grant you the Vulnerability Down and Damage Up buffs. After that, you can pull two more packs of three enemies to the next wall, where another Treasure Coffer is waiting.

Clear the saltcrystal strings: Now, you need to defeat Rhitahtyn the Unshakable. After you beat him, you'll get another Treasure Coffer.

Arrive at the Midnight Downwell: In this area, you'll encounter a pack of four enemies. You can pull them past the next two walkways (don't forget to open the Treasure Coffer you'll find along the way) to reach another group of three enemies. The final passageway is guarded by a pack of four enemies and a Sinking Regret, along with the last Treasure Coffer.

Defeat Amon the Undying: This is it – the final boss battle! You'll face off against Amon the Undying. After you've defeated him, the dungeon is complete! You'll get one last Treasure Coffer before heading for the exit.