climb all the way down (once they reached the edge) and then climb all the way up to bridge? they clearly can make rope strong enough to hold one person so climbing down should not be a problem and then if they walked all around the structure they would see the light on the wall, though not sure if they would be able to climb up, but I think I would rather take my odds with climbing and possible death by falling than the other possible causes of death

all assuming there won't be some doors at ground floor which there should be for sure for practical reasons like cleaning death bodies