Ruined King: A League of Legends Story
52 Achievements
40-50h
GOG
Treasure Diver
Reel in a Treasure cache while fishing
22.7%
How to unlock the Treasure Diver achievement in Ruined King: A League of Legends Story - Definitive Guide
In some fishing spots, you can reel in a treasure instead of a fish. However, the chest looks like a fish so there is no way to know if it's a treasure or not. The first fishing spot in The Buhru Grotto has always a chest (one the most distant fish).
This achievement should happen as you work toward Fishing Journalist (30G). Usually the furthest "fish" in a pond will be a treasure chest, and it will definitely happen before you catch all 30 fish if you're emptying the fishing spots each time.