I found all 8 cursed souls, but I don't know what they do. Maybe I missed something in the text. What do the cursed souls do?
Like Moosh said, the doors are open/closed based on either story mode (each story ends in one of them) or seed (if story is off, the left door is alwats open, and either the right or north is). BUT the cursed skulls/souls are required to open the portals on the other side of those doors.
By the way, what character did you play? Story mode? Did you find the funny statue in the final area?