Nova pushed open the stone gate and discovered a massive underground city inside. The city had towering buildings and complex passages. Though abandoned for a long time, its former glory was still evident. Photon's light illuminated murals on the walls, depicting a powerful civilization fighting against some dark force. Nova carefully observed the murals and suddenly noticed a familiar symbol in the center—exactly the same as the mysterious signal he had received. He realized this signal might be a distress message left by this ancient civilization.