He might discover some long - lost jutsu. Ancient labs could hold secrets to powerful ninja techniques that have been forgotten over time. Maybe he'll find scrolls with unique chakra - based abilities or old - fashioned weapons with special powers.
One interesting take in a fanfiction could be that Naruto finds Orochimaru's lab while looking for Sasuke. He enters the lab full of determination to bring Sasuke back. Inside, he sees the remnants of Orochimaru's attempts to transfer his soul or create powerful hybrids. This discovery makes Naruto realize the full extent of Orochimaru's madness and the danger Sasuke is in. It also gives him more motivation to not only rescue Sasuke but also put an end to Orochimaru's evil plans once and for all.
The lab could hold secrets about Orochimaru's past. Maybe there are records of his early days as a ninja, his training, and what led him to become so obsessed with immortality. Naruto might stumble upon these records and gain a better understanding of his enemy.
Well, Naruto would probably immediately try to free her. He's the kind of person who can't stand seeing someone in distress. He might use his ninja skills to break the chains quietly if he's worried about enemies nearby. Then he'd likely ask her who she is and how she ended up there.
Well, Naruto might first try to free Kaguya. He is a hero after all and doesn't like to see anyone chained unjustly. But he would also be very cautious because Kaguya is extremely powerful and was once a great threat. He could try to communicate with her to understand why she is chained there in the first place.
Another scenario could be that Naruto discovers a hidden chamber in the lab. Inside, there are test subjects that Orochimaru was using for his immortality experiments. Naruto feels sympathy for them and tries to rescue them. However, he has to figure out how to deal with the various traps and security measures in the lab first. He might call for help from his friends like Sakura or Kakashi to assist him in this difficult task.
Naruto would feel a sense of responsibility. He might think that it's his duty to do something about it. He could start by examining the chains to see if there is any way to break them. He would also be on high alert because he doesn't know if this is some sort of trap. He would be thinking about all the possible consequences of his actions and how it could affect the world around him.
He might meet an old hermit who has been guarding the temple for centuries. The hermit could have valuable knowledge about Naruto's parents or some secret ninja arts.