It was no surprise. Billy already could destroy the floor of his house while carrying weights, so it was only natural that he couldn't train everywhere. Training in an open field to let others see him wasn't a good idea either. So, he decided to create a training area really below his house. Otherwise, he will cause tremors and damage it. After brainstorming for a while, Billy had a clear idea of what he was going to do. He needed more...
"I suppose this time I will have to add other things… like magic bubbles and a ventilation system, or things might get too hot down there," Billy thought.
While Billy could train with relative privacy in any dungeon, he couldn't practice anything new or big without risking an accident. The underground training area will be made to do exactly that. Without wasting any time, Billy began to work on that.