what happen in chapter 38?

They find the carving of, "Two letters, which had been engraven three hundred years before." They now have a way to the centre of the earth. They proceed to find Hans. The professor exclaims, "Do you know, my dear boy, that to reach the interior of the earth we have only five thousand miles to travel!" They begin to prepare for their journey. They find a huge rock wall which they need to destroy. They decide to blow the wall down by making a concoction of strong gunpowder.