"Qui'Tu" was a place in Klingon mythology that Spock's half-brother, Sybok, believed he located on a planet at the center of the galaxy. This mythic planet had many names across alien cultures. Sybok believed that a powerful entity existed there, which he called "God", and that all life had originated there. Sybok searched for this planet for many years, collecting a group of loyal fundamentalists as he continued to search.
Eventually, Sybok and his followers stole the starship USS Enterprise-A and used it to travel to where he believed this planet to be. However, he discovered that the entity which he had sought for much of his life was a malevolent being, its only intention to travel beyond the Great Barrier and escape imprisonment. Sybok was killed by the entity, and the being was destroyed. (Star Trek V: The Final Frontier)