An ancient Italian called Signor Bruno took us exploring. He showed how you could make new holes for the hot gases to escape.
He also threw a large boulder onto the ground and it made a hollow booming sound. This was because below us was an enormous chamber covered with a thin solidified lava and ash layer on which we were standing. It boomed when we all jumped up and down as well!
Luckily there were no volunteers to put their fingers into the boiling mud.