If you have been exploring the world of Genshin Impact, then you may have come across the Dunyu Ruins in Liyue. This is an interesting area, as the layout heavily hints that you can lower the water to access the submerged Geoculus.
First things first, you will need to have a Geo character to unlock this puzzle, so make sure you have one in your party.
The first thing you need to do is light four torches that you can find in the area, so for this you will need a Pyro character. You can find one in the main ruined building, near the stairs that run up from the water.
The second one is on the left platform that will be submerged when you arrive in the area.
You can find two near the Geo seal, one directly beside it and the other on a pillar behind it.
When they are all lit, the Geo seal will unlock and you can hit it with a Geo ability to activate it.
Now, to get the chests and Geoculus in the center of the area takes a little more work. Activating the seal will make the water levels drop, but you also need to herd some ghost fairies.
You can find the first ghost fairy can be found beside the torch that is under the building near the stairs. The second one can be found in the upper levels. The third ghost fairy is the problem.
Go down into the newly revealed area and go all the way to the end. Interact with the challenge pillar and complete it to the open the doors behind. Go inside and clear out all the enemies, then interact with with the ghost fairy. It will go through the ceiling, so you need to follow it up by whatever means you can. Climb the walls, or use Venti to boost up through the gap in the ceiling. Take out the next mob and move through the ghost fairy to make it move again. Drop back down though the hole, go outside and you will the fairy to your right.
Move it to the plinth and the shield blocking your access to the chest and Geoculus will finally drop.