You will receive the quest "The Mystery of the Arcadia Ruins" in the Genshin Impact by talking to NPC Keia in the Knights' Quarters in Monstadt. You must help Keiya find his grandfather's treasures.
Start the quest and collect information
As mentioned, the mission starts after you talk to Keia from the Order of Knights. Follow him to learn more about the quest. Next, you need to speak to two NPCs in front of the Adventurers Guild. The target radius is marked on the map.
Then you need to return to Keiya, who will tell you the whereabouts of the informant - you need to meet him in the Whispering Forest. Open the map, teleport to the nearest travel point and run to the entrance to the forest. The informant will come straight to you, but he is being chased by enemies that you need to kill. In return, you will receive the first clue.
Solve the riddle of the Treasure Trail I
Return to Keiya and talk to him. You will learn that you have to look for treasure in the windmills in Mondsstadt. Outside on the map, the mill you need will be marked, which is located to the east of the knightly order.
To climb a windmill, you need all your stamina. If necessary, increase its level by using one of the dishes. Once you're on the top floor, head up the stairs to find a chest with a second clue.
Solve the riddle of the Treasure Trail II
The treasure map shows a lake location south of Kellingen. First, go to Keia to find out more about the solution. Then, head to the lake and notice the waterfall. You need to climb to the left of the waterfall to a higher level. Kill the ice enemies and then attack the torches with a frost attack (cryo). Once you've done that, a chest will appear in the center with the third and final clue.
Decipher the treasure map and complete the quest
The treasure map shows the entrance to the Falcon Coast Cave. Enter Dadaupa Gorge and select the Mystery of the Ruins of Arcadia quest. The recommended size of the army is 10 people.
The dungeon is short and has no mysteries. You just need to run to the goal and destroy enemies in the process. At the end, Keia will suddenly appear, who will say that there are no treasures here.
After the cut-scene, the gate will open and the Guardian of the Ruins will appear, whom you need to kill. His weak point is his head, so the archers have an advantage here. After winning, you will receive a reward from Keiya.
