As Eric and Osira mare their way towards the fifth tunnel, they found a staircase unlike any other here based on the whole experience! The Staircase doesn't sink 20 meters down nor does it rise 20 meters up! To break the usual here, this staircase sinks 40 meters down!
But what would require to sink that deep? Sure there is enough mountain to dig through but is it worth it? The deeper they go the stronger the weighing pressure is from the mountain, or could this just have been a natural cave tunneling down 40 meters so they used it to their advantage. The staircase is surprisingly straight but of course if there is a tunnel to work on, they can carve their way straight and put walls on the side to create an illusion of architectural perfection.