With the new world section “Fontaine” and the associated underwater world, new types of chests and puzzles have also been added. These include the rare chests that are trapped in an algae web. These chests are surrounded by algae and must be freed before they can be opened. There are two different types of chests that are trapped in plants. Both can be opened in the same way. The second chest is just a little harder to free.
These seaweed chests are very easy to unlock, all you need is the Normal Attack in Fontaine’s Underwater World. To get this you have to look for one of the rays that have a blue symbol floating above them. This can be absorbed with the right mouse button and then you have the ability, so you have an underwater attack that you need in Fontaine.
Where to find the Rare Algae Chest?
The Rare (Exquisite) Chest can be found in the Salacia Plain, at the exact location shown in the picture:
Genshin Impact: Fontaine Algae Chest Open
In order to destroy the small yellowish spheres you must first get the ability from one of these rays. The rays can usually be found in the vicinity of the crates. With a right click you can remove the ability from the ray.
Then attack the yellowish spheres next to the chest blocked by plants (E key).
Once both balls are destroyed, the alga disappears and you can open the chest / crate.
This is how easy it is to open the algae chest in Genshin Impact.