Early on in the first act of Baldur’s Gate 3, the player can visit an abandoned temple of Selune (the goddess of the moon) that has been taken over by goblins. With a little exploration, you’ll come across a small room with a puzzle inside it - there are four circular plates on the floor of the room, with four symbols showing full moons, half moons, and new moons on each.
Solving this puzzle will give you access to the deepest reaches of the temple and serves as an entrance to the Underdark, a terribly dangerous area that you really shouldn’t explore until you’ve hit level four and gathered all the best equipment that the surface has to offer - lest you get ganked by a Bullette or some other nasty beastie.
Updated July 27, 2022 by Ryan Bamsey: Baldur’s Gate 3 is getting updates all the time, and now that we have a tentative release window, we’re going over our old guides and sprucing them up. We’ve added some hints to the solution of this nasty puzzle and shown where to find the in-game hints, in case you want to take a crack at it yourself!
How To Solve The Moon Door Puzzle
The clue to this puzzle is found in the Shattered Sanctum, in the room filled with Firewine Barrels and Smokepowder Barrels. There is a mural showing four phases of the moon in a diamond formation, with the full moon on the top, the new moon on the bottom, and half moons on the sides. This room is to the left of Priestess Gut’s room and can be accessed without antagonizing the traders through wooden platforms near the ceiling.
In order to bypass his puzzle, located in the Defiled Temple, you’ll need to rotate the panels so that all of the new moons (the black circles) are moved to the bottom, which is the panel with the light shining on it. The full moons (white circles) need to be moved to the top panel, with the four half-moon icons placed at the four points furthest to the right and left. The best way to do this is to sort out the full moons first - once you have them in place, you shouldn’t need to rotate the top panel at all, just the lower panels.
The image below shows you what the puzzle should look like.
