I'm in the planar sphere and stuck. I've lit the three things on the north east,
I've found the arm of the golem, but not the head. I've kill every living creature
I could find. But I wasn't able to open my last unexplored door, the one you find
at the immediate east of the center west room. So, what to do ? I can't leave the
Sphere...

SPOILER:
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There should be a door (at the east side) in the room where you have to light up the 3 furnaces, which will lead to another room with the golem head.