As for most of the mystery there Indiana Jones and The Great Circle is located in just one area, the Serpent's Chest quest will take you around the world to visit ancient sites. These keys are a bit off the beaten path, so it's likely that you'll find them on your own before you find the snake chest in Voss's camp.

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If you're having trouble following the three keys, this is the guide you're looking for.
How to begin the mystery of the snake's chest
This mystery begins with Sukhothai area of Voss camp. Start with a quick trip to Wat Chana Songkhram, the nearest checkpoint to the camp. Crawl under the wall and to the left, then cross the bridge to Voss's camp.
The Royal Army uniform, which you can see in Voss' camp, makes it easy to get around here.
When you reach the end of the bridge and enter the camp proper, turn right and you will see a green tent on the other side of the truck. In this tent is the breast of the serpent. Jump over the knee-high wall at the end of the chain link fence to find the tent door, enter and you'll find Voss's letter sitting on the table next to The breast of the serpent
Where to find the key to open the snake's chest
As Voss's Letter explains, the key to the serpent's chest was scattered throughout the world. You need to go back to Vatican City, Giza and Shanghai to find each of the three keys, return to Voss's base in Sukhothai to open the chest.
Vatican City Key
The keys to the Vatican City can be found in the underground area below the Research Station. You've probably been exploring this area for a long time, so it's a bit confusing to navigate.
Start by fast-traveling to the Excavation Site and going down into the pit. Use the platforms to break your fall as you descend. When you reach the wide open room at the bottom, turn around and go to the small gap in the wall behind you.
Follow the curve of this corridor, then jump into the hole to fall into the water below. Swim through the door in the water, then continue swimming until you reach a large open room. The corridor continues straight to the left and slightly to the left. Rise out of the water and enter the gap in the wall to enter the cave.
It's easy to get lost here, but if you follow the burning beacon At the end you should see a steep drop with two planks. When you reach the bottom, turn right and crawl through the small hole. Walk forward until you reach a ledge with water on the other side. Above it will be a broken bridge that you can float on, but instead, jump into the water and swim to the far wall.
Dive into the water when you reach the far wall. You'll find a dead center that will lead to a large piece of wood blocking the way forward. Connect with it to raise it, then it pops out of the water. You will see the Ancient Vatican on the floor at the top of the stairs.
Giza Key
The keys to Giza are easier to track than the keys to Vatican City. In the Khentkawes Excavation Site, which is the excavation site with the central elevator where you had to restore the power in the middle of the map between two restricted areas. Go to the center of the mining area where the elevator is.
Instead of going down the elevator, go to the section where the Nazis poured water. Follow the main water pipe from the pump so you know you're doing well. Take the first right and go up the stairs, then make a left into a large open room with all the water. You will continue down the opposite side of this room, being careful to avoid any enemies that may move around.
When you reach the far wall, jump into the water. There is an underwater passage on this wall on the far side that you may have seen on your first visit here. Swim down and emerge on the other side. A light leads you to the left, but dive back into the water and look at the wall on the right. You'll see a piece of wood blocking a hallway. Contact him, then swim to find the Ancient Giza Key on the other side.
Shanghai Key
Backtracking through Shanghai can be difficult. When you revisit the area, it starts where Indy and Gian found the plane. Cross the roof, jump across the gap, and drop down to the building straight ahead to find it still burning.
Once inside, stay to the right and jump over the large hole in the floor. You may get stuck on a broken tree here, but just keep jumping until you're done. You'll then slide across the narrow floor still attached to the wall in front of you. When you get to the other side, turn right, then left, and leave the building.
Once outside, jump on the roof until you reach the fire, then turn right to find a narrow corridor. Go through the connected buildings and continue until you can jump down to the ground. You should now be near a canal and a broken bridge across it.
If you missed it the first time here, there is a comic book called Cold meeting on the balcony to the left of the crashed plane.
Follow the duct to the right until you reach a wall, then jump into it. In the small gap between the sidewalk and the wall, you'll find another underwater passage blocked by planks.
Connect with the tree to move it out of the way, then swim to find the Ancient Shanghai Key on the other side.
The final step is to return to the Serpent's Camp at Voss' camp and open it with three keys, revealing an Ancient Relic inside.
All the notes on the snake's chest
Voss letter |
In Voss' camp, near the snake's chest |
The only note you need is the one that starts the quest, so it can't be forgotten.

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