The Lost in the Past Sukhothai Fieldwork can only be started after completing The Kid Who Vanished Sukhothai fieldwork. After doing so we can return to Sunan in the main village and speak with him.
From here, we will head to the area marked on our map which is Wat Sa Si, then head into the temple to find a stone we can interact with.
We will wake up in this dream sequence, where we first need to take a picture of the hall doors to open them. Then we just want to walk around this circle speaking to characters as they appear and entering different rooms as they open to us.
When we enter the classroom, we will need to complete a basic puzzle. We can place the golden idol in the center of the table, the cat to the left, and the medallion to the right, then snap a picture of the blackboard before returning to the hall to continue the cycle.
Eventually, we will meet back up with Antonio and need to complete the crucifixion puzzle from the Vatican again. Grab the wine and pour it down then drain. Then set the levers to the correct numbers. Both hands should be 2, the body should be 3, then the left leg from our perspective should be 3, and the right leg from our perspective should be 4.
Now that we are on the ceiling, we want to return to the hall to continue the cycle again, looking out for pedestals with Roman numerals on them. Well then need to search for a room where we can place the Roman numerals to create room 11.
After grabbing our hat, a guardian will begin chasing us, immediately turn around and run to the light to escape.
Finally back at the stone we can solve this puzzle, the solution can be found in our notes but we can also kind of brute force this puzzle. As we turn the stones, Indy will say the word when we turn to the right symbol. He only speaks when we find the correct symbol, so just do that for all three stones to solve this puzzle, grab our prize, and return to Sunan in the main village to complete this fieldwork.