Genshin Impact Beryl Region Elynas boiling lake puzzle guide (Precious Chest & Luxurious Chest)

While traveling in Fontaine's Beryl Region, you'll encounter a lake with boiling water south of Elynas. At the center of the lake lies a locked Precious Chest. You must solve a two-part puzzle using Hydrograna to get two Precious Chests, one Luxurious Chest, a hidden Achievement, and access to a Hydroculus.

How to solve the Water Volume Detection Crystal puzzle south of Elynas in Genshin Impact

You can find the puzzle in the boiling lake south of Elynas. Its exact location is circled in the image above. Once you arrive, you'll find a locked Precious Chest at the center of the lake. Be careful as the water is extremely hot and will quickly drain your HP, so avoid swimming in it unless required for this puzzle.

Hydro mechanism #1

First, head southwest of the lake to find a mechanism locked behind thorns. Apply Pyro onto the thorns to get rid of them, freeing the Hydro mechanism (Water Volume Detection Crystal). Then, interact with the Hydro mechanism to move it toward the center of the lake.

Hydro mechanism #2

Next, head southeast of the boiling lake to find a group of enemies surrounding the Hydro mechanisms. Defeat the enemies to unlock the mechanism. Then, interact with it to move it to the center of the lake.

Hydro mechanism #3

Lastly, you need to head northeast of the boiling lake to find an Ousia Block at the top of the tree. Follow these steps in the exact order:

1. Pick up the Ousia Block on top of tree.
2. Attack the Pneumia mechanism using any attack to break it, revealing a Hydro mechanism.
3. Interact with the Hydro mechanism to move it to the center of the lake.

Related: Genshin Impact Hydro Traveler – Skills, Talents, and Rating

Now that all three Hydro mechanisms have been moved, swim to the center of the lake—but be careful not to die from the water. Climb the rock and approach the Hydrograna to pick it up. Make sure your character is affected by Hydro (you can get wet from the water or by using a Hydro skill).

Wait a few seconds for the Hydrograna to swell, turning into a Hydro Core (looks like a barrier). Then stand beside the Precious Chest so that the Hydro Core touches all three Hydro mechanisms. Your character should look like the picture above. Stand the same way for a bit as the mechanisms need a few seconds to activate.

Once the hydro mechanisms activate, the Precious Chest will unlock. You need to loot the Precious Chest immediately to proceed with the puzzle. Opening the Precious Chest will summon a "portal" that you must Enter to be transported underwater. While you're being transported, keep your hands off the movement buttons so you don't get lost mid-way.

How to solve the boiling lake underwater puzzle south of Elynas in Genshin Impact (Precious Chest)

Once you're underwater, ascend to the surface by heading to the shallow water pictured above. Once you ascend, you'll find yourself in an underground cave brimming with Pyro Energy.

You need to approach the locked Hydro mechanism—its exact location is circled in the image above. Defeat the enemies surrounding the mechanism to trigger Hydro lines to appear. These lines indicate the locations of the three Hydrograna required to solve the puzzle, but I'll also show you their exact positions below.

Related: How to Unlock the Fontaine Reputation Board in Genshin Impact

Hydro Core #1

Head to the exact location circled in the image above to find a Hydro rock. Attack it to reveal a Hydrograna, which you need to approach to pick up.

Wait for the Hydrograna to swell into a Hydro Core. If it doesn't happen in a few seconds, apply Hydro on yourself first. Then, head to the nearby mechanism to Install Hydro Core. Its exact location is circled in the image above.

Hydro Core #2

The second Hydrograna is hidden inside a crate located in the exact area circled above. Break the crate using any attack to automatically pick up a Hydrograna. Wait for the Hydrograna to swell into a Hydro Core. If it doesn't happen in a few seconds, apply Hydro on yourself first.

Next, approach the nearby mechanism (exact location pictured above) and interact with it to Install Hydro Core.

Hydro Core #3

Head to the exact area circled in the image above to find a row of three Cryo Barrels. Destroy all three Cryo Barrels to reveal three Hydrograna. Approach them to pick up all three. Wait for the Hydrograna to swell into a Hydro Core. If this doesn't happen after a few seconds, apply Hydro on yourself first.

Once that's done, approach the nearby mechanism to Install Hydro Core. At this point, the Hydro Monument will unlock, allowing you to proceed with the puzzle.

Hydro Monument, Precious Chest, Luxurious Chest

Return to the Hydro Monument from earlier. As it's now unlocked, apply Hydro to activate it. Doing so will prompt the water level to increase, submerging the entire area underwater.

Swim toward the "portal" that has appeared beside the Hydro Monument and enter. You'll be propelled further into the cave.

You'll land in front of a Precious Chest. Don't forget to loot it! You can ignore the enemies and continue swimming to proceed with the puzzle.

Swim toward the water current in front of the Precious Chest, which will force your character to ride the current. You can use the directional keys to change the camera angle, but allow the current to take you to your destination.

The current will take you to a small section housing a Hydroculus. I recommend claiming it now as it will be hard to get to this area later on. When you're ready, ascend to the surface of the water to find another underground area on land.

Enter the land area and follow the path forward. You'll eventually encounter another "portal." Enter it to get teleported back to the boiling lake, which has now been cooled down. You'll get the Wonders of the World Achievement called "Core Cooling."

The rewards don't end there. In this puzzle that keeps on giving, you can claim a final reward: a Luxurious Chest inside the newly-cooled lake. Dive underwater to claim your loot. There's also an Exquisite Chest nearby, so don't forget to loot it as well.

For more on Fontaine, check out our guide on How to win the Trial against Marcel in Genshin Impact – As Light Rain Falls Without Reason here on Pro Game Guides.