Avatar: The Last Airbender saw Aang and his friends travel all around the world as they visited the most fascinating locations it had to offer, and along the way, perhaps the most interesting of all was Wan Shi Tong's Library. Located in the harsh sands of the Si Wong Desert, the wealth of knowledge was rumored to only be a legend during Aang's Era. After Aang and his friends angered Wan Shi Tong, the great owl pulled his repository of wisdom into the Spirit World, where it remained in The Legend of Korra.
However, Avatar Legends: The Roleplaying Game offers insight for the first time into what the great library was like in the centuries before Aang arrived there. It was already one of Avatar's most intriguing locations, and the Avatar Legends expansion delves into that intrigue head first.
While venturing across the Earth Kingdom, Aang and his friends came upon word of a mythic repository of knowledge tucked away deep within the Si Wong Desert. Although it was thought by some to not even exist, with the aid of their flying bison Appa and a local guide, the Gaang managed to find out that the myth was very much true. Inhabited by an ancient spirit of knowledge known as Wan Shi Tong, who introduced himself as He Who Knows One Thousand Things, the library provided unparalleled depths of knowledge found nowhere else in the world. Sokka hoped to use that knowledge toward his and his friends' advantage in winning the One Hundred Year War.
However, there was one major problem: Wan Shi Tong forbade anyone from perusing his tomes for any purpose other than the sake of knowledge itself. Sickened with humans after the last man who used the library (later revealed to Admiral Zhao) burned a section of it to benefit the Fire Nation in the war, Wan Shi Tong warned the Gaang of consequences if they proved similarly selfish. And consequences there were. When Sokka discovered the Day of the Black Sun that would later help their war efforts, Wan Shi Tong became enraged and pulled the entire library back into the Spirit World as his suspicions over humanity were affirmed. Still, Avatar Legends indicates that Wan Shi Tong's relationship with humanity was not always so fraught.
In the Era of Kyoshi, centuries before Aang, Wan Shi Tong's Library inhabited the same place in the Si Wong Desert while being far more accessible to the humans who sought it out. With several of its towers and spires visible, Wan Shi Tong openly allowed anyone seeking the library out to peruse its halls. While still wary of humans, in those days, Wan Shi Tong proved far more trusting, and the sandbenders of the Si Wong often made a tidy profit from ferrying others through the dunes to the library.
However, that relationship soured as those the Si Wong tribespeople brought the Wan Shi Tong's library abused his knowledge, much as Aang and his friends would in the future. By the time of Roku's Era, the library became more secluded than before as the surrounding sands began to swallow it up. Wan Shi Tong proved even warier of humanity than he was previously, and were it not for the valuable information his knowledge-seeking foxes brought him or the few secrets shared by the travelers who managed to make the trek, he may have not remained at all. The Si Wong tribespeople were banned from access altogether, but allowing anyone else would be a mistake Wan Shi Tong would barely tolerate by the time Admiral Zhao arrived during the Hundred Year War Era.
The difficulty Wan Shi Tong had in receding from the human world always came in his irresistible curiosity about the knowledge humans could bring him. Admiral Zhao apparently bought his way into the library by offering knowledge of Fire Nation war machines, but the cost of that knowledge ended up being Zhao burning away an entire section pertaining to Fire Nation secrets.
There remain plenty more secrets about Wan Shi Tong's Library, and fans do not yet exactly know ten thousand things. However, with the release of the Avatar Legends expansion, they are certainly closer than ever before.