From Tori Wiki
Chests are a type of item that can be opened at Backpack Unlocker's Hut to receive other items. Unlike Containers, chests require an Any Key to be opened.
How to Use
A chest is used by opening it at Backpack Unlocker's Hut to get the items inside. Opening a chest requires an Any Key. Just having an Any Key in your inventory when you open the chest is enough. Any Keys can only be used once, and multiple keys are needed to open more than one chest. Each chest has its own set of items you can potentially find in it. To see what items a chest may drop, please check its individual page or this spreadsheet.
List of Chests
|Name||Chest||How to Get|
|Crystal Chest||Cold Valley (digging)|
|Forest Chest||Green Valley (digging)|
|Sea Chest||Very Common Beach (digging)|