The moon is an object above the first layer of the Work (Sky), composed of a unique material named "cheese". In the center of the Moon, glyphs can be found that read "Converge the edges" which is a hint telling the player to collect the Essences and bring them to the Moon.
"Opening" the Moon
In order to "open" the Moon, the player must bring a combination of the 4 Essences and dig inside its center to activate one of the 3 unique events.
The Void Event
If the Essences of Air, Fire, Earth and Water are brought to the centre of the Moon, the entire Moon will transform into void liquid and the message "The four essences reveal their secret - - - The moon's egg cracks open and it's contents have been unlocked" will appear.
This is the best way to get a sizeable amount of void liquid.
The Drunk Event
If the Essence of Spirits is brought along with the other Essences to the center of the Moon, the entire Moon will transform into whiskey and show the message "The four essences reveal their secret - - - The moon spills and unlocks it's inebriating contents" .
Activating any of these events will unlock the Destruction spell.
The Golden Event (Spoiler Warning)
If the Sampo is taken to the Moon alongside the elemental Essences, the Work will be completed, and the entire world will turn into gold without killing the Noita in the process, regardless of the amount of Orbs of True/Corrupted Knowledge they have. The gold counter becomes an infinity symbol. The message is the same as in the Void Event.
The Gourd Event (Spoiler Warning)
Throwing a Refreshing Gourd at Kolmisilmä will deform its body into a gourd-like shape and turn it green. Bringing the transformed Final Boss to the Moon along with the elemental Essences will transform the Moon into Healthium, and from its center, Touch of Blood, Touch of Gold, Touch of Oil, Touch of Smoke, Touch of Spirits and Touch of Water will drop. There is no message.
Coordinates
The Moon has been found on x = 264 and y = -25839 (y axis goes down).