Tau Alpha C was a planet located far away from Federation space, and was home to a humanoid race, of which 1% is made up of Travelers. When a potential Traveler is about to be "born", they were brought back to Tau Alpha C to meet their "mother", as well as undergo the final tests, which include gazing into the Pool of Prophecy. (TNG episode: "Where No One Has Gone Before", TNG novel: A Time to Be Born)