>Later, after the water had run off, you could see that down at the bottom, where the boys walked in, there were much larger gaps. But the divers couldn’t attach anything to the muddy bottom when laying out the guide lines. They had to follow along the ceiling. The only path they found was through the narrow passageways.

As I understand it, they had to use the narrow passages at the top because they were not able to discover the wide gaps near the bottom. I assume some equipment could help with that making the transport easier once a more comfortable path was found.