The dilapidated altar in the cave of the Unnamed island (Divinity: Original Sin 2)

Here is screen of the place

Spoiler

Nope, tried the rain of blood, tried to kill partner, nifiga

the head of Alexander on the altar or Alexander will send for the head of Sallow Man'a(playing the English version), giving the hood of crucita(use a hidden door behind the altar)

On the altar it is necessary to place the head of Bishop Alexander or Bellicose, depending on the chosen path

Yes thank you all for the advice, he came later than before.

the passage can be open with the hood true vision, falls from Alexandra

Di Dracula
If peace with Alexander, he this hood himself will give.