???? is a secret location in Phoenotopia situated near the Hidden Village. It can only be accessed by achieving 100% completion of the game (see the list on that page for the requirements). After that, you have to talk to Gill in the Hidden Village to unlock this location on the World Map.
As it is located near the Hidden Village, ???? is a forested area much like the village itself. It is a relatively small area with no enemies whatsoever and no objectives other than to reach the top of the level, after which you will receive the Last Song of Earth achievement.
Upon entering the area, you will find yourself at the foot of a small mountain. To climb it, you'll have to use the Javelin to climb the stone walls and use the Artifact to reveal some invisible platforms that can help you climb up further. At the top of the mountain there is a passage blocked by stones that must be blown up with Bombs or a charged Javelin. Once that's done, you can enter the mountain and go into the next room, which features four strange capsules embedded into the cave wall. Once you approach the capsules, a song called The Last Song of Earth will play and you'll get the achievement of the same name. You can also go farther to the right to the other side of the mountain, where you'll find a cliff with a beautiful sunset view in the background.
- Aside from Mul Cavern, this is the only location where the Blue Wisps appear spontaneously rather than being limited to Save Shrines.
- The Last Song of Earth is the only song in the soundtrack that is unlisted, though it becomes available after purchasing and downloading the soundtrack.