I recall a fanfic called 'Sentient Library: Naruto's New Ally'. In it, the sentient library is a sort of magical entity that has been observing the ninja world for ages. When Naruto finds it, it offers him knowledge that was lost over time. It shows Naruto different historical events through magical books, which gives him an edge in battles and also in understanding the politics of the ninja villages.
It could have Naruto discovering long - lost jutsu in the Uzumaki library. Maybe some ancient scrolls that hold the secrets of powerful chakra control techniques.
He might meet the spirit of an ancient ninja who was the keeper of the library. This spirit could guide Naruto through the library and teach him things that no one else in the present day knows.
Perhaps in this fanfiction, the secret library is guarded by some sort of magical or powerful entity. Naruto, being Naruto, would try to befriend it first. Once inside, he could find prophecies about the future of the ninja world written in the books. This knowledge might put him on a new path of preventing future disasters and bringing about a new era of peace in the ninja world.
Well, he could gain new powers. Maybe the sentient library has books that teach him long - lost jutsu or give him knowledge about the nature of chakra that no one else in the ninja world knows. For example, he might learn how to combine different elemental chakra in a completely new way.
Some Naruto - centered forums might also be a good place to look. Fans often share their fanfictions there. You can engage with the community, ask if anyone has come across a fanfiction about Naruto finding the Uzumaki library, and they might be able to point you in the right direction.
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.
He might meet an ancient sage who has been sleeping in the ruins for centuries. This sage could have a vast amount of knowledge about chakra and the ninja arts that Naruto could learn from.
Well, it could be that Naruto finds a connection to an old shinobi clan in the ancient temple. This discovery could lead him on a new adventure to learn about their history and techniques. There might also be a spirit or an old sage in the temple that imparts some wisdom to Naruto, helping him become a stronger ninja.