Mystery of the Arcadian Ruins is a quest you receive at the very beginning of the game Genshin Impact. Unlike most tasks in the game, there is no marker that will precisely show you where to go. With the help of this guide, you can easily solve the mystery and open all the chests needed to complete the quest.
You can get hints from Kaeya outside the Adventurer's Guild, but even they won't give you the exact location of the chests. This guide will help you crack the code and decipher the locations based on the cryptic hints.
To start the quest, find Kaeya in the Knights of Favonius Headquarters. Talk to him to start the Secret Pirate Treasure quest chain. He will send you to the Adventurer's Guild to collect evidence. Talk to Cyrus who stands in front of the Adventurer's Guild building, and you will be sent back to Kaeya. Upon returning, you will complete the Kaeya's Troubles quest and start the Mystery of the Arcadian Ruins quest.
Kaeya will send you to meet his informant outside Mondstadt in Whispering Woods. At the location, you will find that the informant is being attacked by a group of enemies. Deal with them and talk to the informant. She will give you a picture with a riddle that will lead you to the first treasure chest. You can return to Kaeya at the Knights of Favonius Headquarters for a hint, or you can simply continue following this guide to find the exact location of the chest.
The first clue reads: In the city on the lake resides three six-armed giants. Two guard the statue, one the treasure.
This clue refers to the three windmills in Mondstadt. Climb the southwestern windmill. If you can't find the way, just climb the nearest building and glide to the destination. At the top, a chest awaits you. Inside, you will find another map with another clue. Your treasure hunt is not over yet.
The second clue will take you a bit further, but still not too far. The clue reads: She doesn't love him at all. The passion rushing through the clear spring is just a front. When she's cold and alone, her true heart is revealed.
You can return to Kaeya at the Knights of Favonius Headquarters for a hint. He will advise you to head to Springvale, a region south of Mondstadt, which will help narrow down your search. The clue map should guide you to the destination, but if you can't find it, it's near the Springvale water body on your map. At this location, there is a waterfall, and near the waterfall, you will find three short pillars with ice symbols on them. You will need to freeze them using Kaeya's cryo abilities to summon a chest containing the final clue.
The third and final clue will mark a new point on your map. You won't need to do any detective work to figure out where to go next. Head to Falcon Coast, and you will find a dungeon in a cave by the beach. The recommended level is 10, so make sure your party members are strong enough before entering.
This is a fairly standard dungeon, but you will be able to use Kaeya's cryo abilities to disable fire traps and defeat fire enemies. At the end of the dungeon, you will face a boss battle, but you should be able to handle it. After landing the final blow, the quest will be completed.