You might come across Rosymorn Monastery as you near the end of Act 1 in Baldur's Gate 3. This is when you get the choice between travelling through the Underdark or taking the mountain pass to get to Moonrise Towers. If you choose the latter, you'll find the run-down monastery off the main track, along with a fairly tricky puzzle to solve.
If you ignore the sideroads and keep heading up the main mountain path, you're going to find yourself up against a tough fight, so heading to the monastery first will make things a little bit easier once you're ready to push on. With that said, here's how to solve the Rosymorn Monastery puzzle and each of the ceremonial weapon locations.
How to solve the Rosymorn Monastery puzzle
From the Rosymorn Monastery waypoint, climb up the vines nearby, then hop over the gap and break the boarded-up section of the building ahead. You'll need to fight a group of Gremishka—magic apparently makes them angry, so be careful—but they're not too tough.
From there, head out through one of the doors on the opposite side of where you entered, turn left, then right at another boarded-up section. Follow the path to the left and you'll find yourself in a room with a circular stained glass window on the floor and four altars around the outside of the room. One of these altars has two glowing blue lights on the front and a Ceremonial Longsword on top of it.
If you examine the stained glass window, you'll notice each quarter of the circle depicts a keeper holding a weapon. The one closest to the altar with the sword is holding a sword, so to solve the puzzle, you need to find the weapons for the other altars.
Here's how to solve the stained glass window puzzle:
- Warhammer: Northeast
- Longsword: Northwest (already placed)
- Battleaxe: southwest (broken piece)
- Mace: southeast
If it helps, you can use the tactical view (press O) to help orient yourself: the minimap has the compass markers on it too. I used the Throw command to place the weapons, as I couldn't find a more elegant option.
Once you've placed all the weapons, you'll get the Morninglord's Radiance buff which causes your weapon attacks to deal additional Radiant damage. It's handy for a battle ahead if you're planning on heading further up the mountain pass.
Ceremonial Warhammer location
From the puzzle room, retrace your steps and break the boards you passed (Fireball works fine for this) then climb the vines immediately to your left. Once at the top, turn left again and head up the steps. If you pan to the right, you should see a couple of eagles guarding a nest and that's where you'll find the Ceremonial Warhammer.
Save your game before you approach then head up the steps. As you get near, one of the eagles will get annoyed: you can try Animal Handling, though the difficulty class for the roll is high at 18, or you can attack the bird. I don't have Animal Speech, so you might be able to talk the eagle around, but I chose violence. Just be careful here as the eagle can easily yeet you—or one of your party members—off the edge of the building.
Once they've been taken care of, pick up the warhammer and head for the next weapon.
Ceremonial Mace location
To find the mace, head back to the vines you climbed up to get to the warhammer but instead of going back inside, head to the far side of the courtyard and jump across to the grassy outcrop. Turn left here and you should spot an opening in the building just ahead of you on a lower level. Jump down here and it's a good idea to save again when you get to the bottom.
The room ahead is full of Kobolds. You can take them by surprise if you use a ranged attack and there are plenty of flammable barrels that you can shoot to help you out if needed. Despite their numbers, this is an easy fight, especially if you stay at the entrance and let them come to you.
Once you've taken care of them all, you'll find the Ceremonial Mace on one of the Kobold's corpses, so be sure to check each one.
Ceremonial Battleaxe location
From the puzzle room, head back to the section outside in the hall where the floor has fallen in and make a jump across the gap to the floor. You'll find an enchanted door just around the corner. It's locked, but despite appearances, you can just use a regular lockpick to open it before breaking the furniture blocking your way.
You'll need to fight the Guardian of Faith inside but he's not hostile until you attack him. If you try to pick up the Ceremonial Battleaxe at his feet, you'll also initiate combat. He has pretty high defence but your best bet is to just pelt him with ranged attacks while keeping outside of his circle. Once he's been destroyed, you can claim the battleaxe.