I have been trying to find these two runes for over an hour now. I just finished the mission where I killed the High Overseer, and I got back to the safe house place. After I woke up, I equipped the heart and now it seems that there is two runes under the rocks, about 5 meters apart. I can't find any way to get in there! I also used the vision where you can see through things and there are two people coughing down there. Is there a house that has been barricaded off? If so, where do I get the key to it?
*UPDATE*
I found a little square thing on the ground nearby, but it won't open when I press F or when I whack it with my sword, and I also tried throwing two grenades at it.