After completing a certain puzzle, you can get an Old Sketch from the ground. In this sketch, it hints towards a location for a buried treasure chest. Here's how to get it and the location.
Where to Get the Old Sketch
Teleport to Beacon near Donglu Research station and go to the buildings submerged in water at the Forgery Challenge. You need to complete the puzzle here to drain the water and access the room at the bottom. The puzzle seems complicated, but it's actually pretty easy.
In short, you need to activate 3 Induction Cell Sockets to drain the water. If you already drain the water, just go to the room at the bottom to get the Old Sketch. If not, you can follow the guide below.
First of all, take the Corroder and go to the opposite building (I'm calling it room 1) to the Spikes to destroy it.
Then, go to another building (this is room 2) with breakable rocks at the front. Break the rock to get into the room and get another Corroder. This will make room 1 which was blocked by the Spikes to be open.
Get into the now open room 1 take an Induction Cell and slot it into the Socket just outside room 1.
Go inside the previous room 2 (where you get the Corroder) and get the Induction Cell before slotting it into the Socket near the room with a locked gate (now this is room 3).
Enter the room 3 and you will find another Induction Cell. Take the cell and slot it into the Socket just outside this room.
Now take back the Induction Cell that you use to open the locked gate at room 3 and slot it into the last Socket near room 2 where you get the Corroder. The puzzle is now completed and the water will be drained.
Inside the room at the bottom, you can Inspect the ground for an Old Sketch.
Where is the Treasure Inside the Old Sketch
Once you get the map, go to the west of this location and you can see a lone chair near the river. There should be an Inspect option so you can just dig out the treasure.
