Naruto might run into a group of rogue ninjas who are using the bunker as their hideout. This would lead to a confrontation where Naruto has to use his skills to defeat them and protect the village from their potential threats.
Perhaps he'll meet a spirit or a ghost in the bunker. It could be the spirit of a former great ninja who imparts some wisdom or a special ability to Naruto to help him on his journey. The spirit could tell Naruto about events from the past that are relevant to the current situation in the ninja world and give him guidance on how to face future challenges.