I think it's just behind the rock face of the main cavern.

They followed the King, leaving the hubbub of the main cavern behind.

"Can you find your way to the main cavern?"

He gestured back to the entrance to the main caverns.

He led the way across the main cavern and down a smaller side passage.

At Mark's reply he led the way to a smaller room off the main cavern.

We can get to the main cavern through any of them.

The second man, illuminated by the light in the main cavern, was still moving.

The last of the light from the main cavern and the re-erected force field had long since died away.

The troop filed through the last door into the main cavern.