The Sukhothai fieldwork A Study In Fear will unlock automatically after progressing the main quest here past exploring and escaping the Hidden Pyramid. After doing so, return to the main village and speak to Pailin.
From the village we will travel to the explosion site which will now be marked on our map and need to make our way through the underground temple following the linear path.
After meeting Annika, we can take the circle key from her and use it on the nearby pedestal to solve a puzzle. We will get more keys as we get deeper into the temple but the idea of every puzzle is to line up all the shapes. Each key will have a shape or multiple shapes and using them will cause the shapes to stop rotating while the rest will remain moving. We then just need to remove the key in time when everything is lined up.
For our second pedestal puzzle, we can grab the Cross and Circle key from the floor in this room and can open the pipe with our whip. Then we will first use the Cross and Circle key from our inventory to line up the Cross with the diamond. Then use the Circle key from our inventory to line up the circle with the rest of the shapes.
After opening the sarcophagus, the ceiling will start to close on us but some spikes will fall down. We can grab one to use on the breakable wall. This will cause the room to begin flooding, allowing us to swim to the escape.
In the final chamber, we have three puzzles to solve and can start with the one on the left. Using the Cross and Circle key from our inventory, line up the cross and circle with the rest of the shapes.
Before tackling the puzzle on the right, we need to use our whip to open another pipe and do some climbing to grab the Cross and Diamond key from a birds nest. Then for the puzzle on the right we want to first use the Cross and Diamond key from our inventory to line up the diamond and the line. Then use the Cross and Circle key to line up the cross with the Diamond and line. And finally use the circle key to line up the circle with the rest of the shapes.
For the final puzzle in the middle, we will first use the cross and circle key to line up the cross and Diamond. Then use the cross and Diamond key to line them up with the line. And finally use the circle key to line up the circle with the rest of the shapes.
As we escape the temple, we want to return to the main village and speak to Pailin again to complete this fieldwork.