Icara, known as the white witch, tasks you with this , after you complete: "Find the Witch". Go Southwards, in the Lucalla forest, and take the path to the North-East, into the mines. If you encounter goblins along your path, this will mean that you are on a good way. They should not be too much of a challenge, because you encounter a larger group of these only once, but they are asleep. Then, try to sneak past, quietly without waking them up. In front of the mines entrance, you encounter the cultists from the village, who cooperate with the goblins. Kill them and enter the mines. You need to explore the mines but, you need to watch out, because there are death knights around, who are immortal. To pass them by, you need a good rogue, or an invisibility spell, which you can buy in your domain, if you bought the hall of the wind.
First of all, you need to complete the "Miner Control" quest, to obtain the password for the gates to the temple ahead. Then, choose one of the characters to sneak to the South-East (while looking at the map) to find the huge gate. Once you find it, say "Sadakandras", and the gate will open. Inside, you meet a woman who created those knights.
After a conversation, she summons three more but, they are terribly slow and you will be able to escape from them. Climb up the stairs, until you see a passage blocked with some junk. Quickly, smash the junk and run up to the green portal. First, choose the portal to the library, run ahead towards the other mirror. There, take the portal to the officer's office, you will get there, without any problems but, soon it will turn out that it is the laboratory of the creator of the knights of death.
Search the room for the "Leandra's Spell", which should be on the desk. Collect it and return to the portal. Now, select "Crypt", and then immediately "Entrance hall", on the same portal.
Finally, keep running ahead, along the narrow passage up to the last teleporter, which will take you outside. In order to find the flask with blood, you need to complete "The Initiation/Infiltration the Imaculates".