After further inspection he realized that this was a bomb shelter. It was made years ago to protect people from any bomb last and hence it was underground. John was shocked to know that a bomb shelter has been living for all those years beneath his own backyard. He also found out electric fan. This made clear that people who made it, took proper care of ventilation as there were vents available. People must have been trapped here for long.
John was super amazed by all this and he wanted to know more.