The Triangle Key is an item found in Broken tooth Island inside of a cave near the ancient society's ruins. The player can find this item by opening the secret door in the ruins. Said secret door is opened by lighting the three unlit Ancient Flares inside. The door will open and the key can be obtained.
The Triangle Key's sole use is to open The Triplicate Space.
Triangular Room[]
The Triangular Room is behind a secret door in the Ancient Ruins, It's sole purpose is to present the Triangle Key.
Although you can't enter behind the rock pillars in this room by jumping, you can get above them by using the Lunchpad, Behind these pillars, It shows a statue of a Grumpus, just like the statue in The Triplicate Space.