This is the Miner's Hat location.

Found on a dead body behind a caved in area inside Beryl's Dream mine. Push the plunger to set off the TNT near the entrance. This will open up an area behind the rocks where you will find the body with the Miner's Hat and the Wide Blade Knife

Found hats are unique hats that can only be found out in the world. They are permanently stored in your wardrobe when you find them.