The Pool of Knowledge was a Force nexus located on a planet in the Maw. It was also located in a realm of the Force known as beyond shadows, which was reached by separating one's mind from one's body. The Pool of Knowledge appeared as a dark pool in a dank grotto.
According to the Mind Walkers, it offered knowledge of all of the past and future if bathed in. Simply gazing upon it allowed Force visions, including the sight of the Throne of Balance. Both Luke Skywalker and Jacen Solo were offered the opportunity to bathe in the Pool of Knowledge, and both declined, instead merely viewing the Throne of Balance.
Later, the Sith Meditation Sphere Ship brought Skywalker and his son there along with the Sith Sarasu Taalon, Gavar Khai and Vestara Khai. The Pool began to show images of the Sith's homeworld of Kesh, then of a Jedi Queen on the Throne of Balance. Taalon demanded to know who the Jedi queen was, as he believed that Jedi might prevent the Sith from ruling the galaxy.
The Skywalkers attacked the Sith to protect the identity of the queen, who was actually their own relative, the daughter of Jacen Solo. Taalon bathed in the Pool, but the Skywalkers managed to escape from the Sith. Due to his time in the pool, Taalon began to transform into an entity like Abeloth.