The Korriban Core was a huge, ancient Sith library that was left by the old masters of the True Sith. The library contained all the teachings of the Sith and Jedi, and included some long-lost lightsaber styles employed by the Sith. The library was regarded as the largest learning center of the galaxy around the Legacy Era.
The Korriban Core was similar to the Trayus Aademy, albeit several times larger. The Korriban Core appeared on the outside as a massive cathedral-like structure. On the inside, the Core was a massive temple lined by rows and rows of texts, holocrons and other recording materials. The center of the core was an elaborate chamber, illuminated by a massive lightsaber crystal hanging like a chandelier.
The Core was once the knowledge bank for the True Sith, up until their departure from known space. As a result, the Core was forgotten and only cryptically mentioned in few texts. In the year 4,136 BBY, the current Dark Lord of the Sith, Darth Pentar, sought the Korriban Core for its secret mass-destruction device. Following Pentar's death, his apprentice Darth Aerie sought the Korriban Core for her master. In 36 ABY, it was found by Darth Aerie and made into her base.