Crystal skull locations

[JoiseyDragun]

So I dont have to waste the entire ♥♥♥♥♥♥♥ day finding statues to pray to just to do part of a quest to get some kinda map, could I get a general list of areas that have Crystal skulls in them? I need three more to finish the set.

[Dan]

If you do the Brahma puzzle you can get them shown on your map.

But there's one hidden near the Underworld COB entrance

[wildfire393]

There are two methods that can help significantly in finding the Crystal Skulls.

The first is equipping the La Mulana 2 app along with both Map apps to show hidden rooms. (You find it In the Eternal Prison, use Thor's Hammer in the room with Neti, the former guard)

The other is completing Brahma's Puzzle, which adds icons for every unfound Crystal Skull to your map.

I believe that the three hardest-to-find skulls are:
Valhalla - The treasury room. Incant Earth + Moon + Heaven in front of the True Throne in Valahalla (the room that says "Sit to proceed"). This opens the floor in the center-bottom room where you fought that miniboss. Depress the switch to unveil a seal that opens the chest
Ancient Chaos - Directly below the grail point. You need to damage the blue-eyed statues on either side of the room simultaneously. Lamp of Time makes this trivial or you can do it with bombs. Once in the room, stand over the chest and it will open. Don't depress the switch or you face a wall of Red Judgment Eyes
Eternal Prison - From the Corridor of Blood entry, jump through the top left of the wall. There's a room you have to try to navigate where there floor is concealed and full of holes, jump your way across. In the next room, jump left and hold against the wall as you fall and you'll fall into a niche. Drop a weight in this hidden niche and it opens the chest

[Wild Matsu]

There is an error in your first listed skull. The correct mantra combination is Fire+Earth to get into the Valhalla Treasury.