To gain entrance to Lucian's Crypt without following the Path of Blood you need to have the "Source Amulet" and the "Scroll of Atonement." Once you have these items and you are inside the room with Lucians statue you need to use spirit vision to see the spirits in the room. Then you equip the "Source Amulet" and absorb the souls until your character says the amulet it full. Now if you are facing the Lucian statue you go left and you will perceive and button on the wall that requires you to put the amulet in and then read the scroll. Finally, a hatch will be discovered that you can enter and when you enter it the achievement will pop.