Genshin Impact Where Once There Was a Calculation Array quest guide

Where Once There Was a Calculation Array is part of the Chronicler of the Crumbling City quest series in Genshin Impact. This quest takes place in the Ancient Sacred Mountain region, located beneath the Giant Volcano of Tollan.

After completing The Frozen, Rekindling Land quest, you will be taken to the depths of the Ancient Sacred Mountain, where a large Secret Source Servant will unlock a few sub-quests needed to complete the Chronicler of the Crumbling City quest series. One of these is Where Once There Was a Calculation Array.

Follow this guide to learn how to complete the Where Once There Was a Calculation Array quest in Genshin Impact.

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Genshin Impact: Where Once There Was a Calculation Array walkthrough

Chronicler of the Crumbling City World Quest Series
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Genshin Impact In Search of a Hidden Heart quest	Genshin Impact Once, the Sacred Seat of Judgement quest	Genshin Impact Where Once There Was a Calculation Array quest
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The Where Once There Was a Calculation Array quest location (Image via HoYoverse)

Where Once There Was a Calculation Array is unlocked after you talk to the big Secret Source Servant as part of the In Search of a Hidden Heart quest.

After starting the Where Once There Was a Calculation Array quest, a location will be marked on your map. To get there, go to the teleport point next to the big Secret Source Servant who gave you the quest and start heading south.

Previous quest: Genshin Impact Once, the Sacred Seat of Judgement quest guide

This Region's Abyssal Corrosion Level (Image via HoYoverse)

Once you arrive, you will find another teleport point and a boss bar displaying This Region's Abyssal Corrosion Level. A few rifthounds will be attacking a small Secret Source Servant. Defeat them to progress the quest.

Secret Source Servant takes you to this entrance (Image via HoYoverse)

Then, follow the Secret Source Servant you just saved. It will lead you down to a cave with a corrupted Secret Source Dragon. Defeat all nearby rifthounds to remove the abyssal corruption from the mechanical dragon.

Fix the Secret Source Dragon (Image via HoYoverse)

The Secret Source Servant will then activate the dragon. You can resonate with the Secret Source Dragon and shoot explosive attacks at Oozing Cores. Destroy all Oozing Cores to fully activate the dragon and then leave the cave.

Bring down the Oozing Cores (Image via HoYoverse)

On your way out, you will need to destroy more Oozing Cores. After you have done so, the Secret Source Dragon will descend to the ground. Go to the altar and click Start to remove the abyssal corrosion completely.

Finishing the quest (Image via HoYoverse)

With that, you have completed the Where Once There Was a Calculation Array quest in Genshin Impact. Completing it rewards you with one Phlogiston unit and three loot chests (1 x Precious, 1 x Exquisite, and 1 x Common).

After finishing this quest, you will unlock the Where Once Force Was Reversed quest in Genshin Impact.