A Miner's hat.
Always identifies and reveals adjacent rooms on the map. Secret Rooms and Super Secret Rooms will be identified with the corresponding discovery sound effect as well when passing by. This will also reveal rooms containing a mini-boss or the Sacrifice Room on the map, though without any signal, when you pass by.
Considerably less useful when Curse of Darkness is in effect. The discovery sound effect will still play (but only once as always), which can help you narrow down the location of the secret rooms.
- If the player has the X-ray Vision, the Spelunker Hat may still be slightly useful to detect the presence of minibosses in a room (such as Greed in a secret room) before entering. If the player also has the Compass, however, Spelunker Hat is redundant.
The name is a reference to the term Spelunking, with the hat representing equipment used.