Credit for this idea goes exclusively to a site commentor by the name of Jason. Thanks for sharing your ideas!
Do you remember Wan Shi Tong’s Library from Book 2 of The Last Airbender? If you don’t, let me refresh your memory: Wan Shi Tong’s Library appeared in an episode called ‘The Library’ in which Aang and the gang traveled to a partially underground library in order to find information on how to defeat the Fire Nation. Ultimately, the Library helped Aang and the gang learn about ‘the day of black sun’ in which an eclipse made Fire Benders bending-less. With this knowledge, Team Avatar helped device a plan known as the Invasion. Even though the plan ultimately failed in the end, it still showed just how useful the Library was to knowledge-seekers.
Something worth noting is that the Library didn’t just contain information on the Fire Nation. It also contained information on a vast variety of topics, one of them being Spirits.
As we all should know, Book 2 of The Legend of Korra is titled Spirit: we will learn all about The Spirit World, the Avatar State and even Spirits in general. I’ve already speculated that Aang could have a major role in guiding Korra on her journeys to The Spirit World, but he probably won’t have all the answers she’s looking for.
Fortunately, Wan Shi Tong’s Library will.