In Star Trek III: The Search for Spock, Spock's regenerated body is found on the Genesis Planet.
The planet is formed by the Genesis Device, which detonates at the end of Star Trek II: The Wrath of Khan. Because Spock transferred his katra, or living spirit, to Dr. Leonard McCoy before dying, his friends learn that his physical body may have survived the Genesis effect.
Admiral Kirk and the Enterprise crew discover that the device regenerated Spock's body from the torpedo casing containing him. Spock appears first as a rapidly aging child, then as an adolescent and young adult as the planet's unstable environment accelerates his development.
The Genesis Planet is not simply an ordinary world with Spock on it. Its changing conditions become central to the story, while Klingon commander Kruge seeks the Genesis technology. The planet is eventually destroyed when its unstable matrix collapses, but Spock is rescued and later restored through the Vulcan fal-tor-pan ritual.