Platonius was a class M planet, home to the Platonians. When the USS Enterprise visited this world, its inhabitants tortured the crew members that beamed down, including Captain James Kirk. (TOS episode: "Plato's Stepchildren") When he was transported downtime from 2270 to 2020 and into Shaun Christopher's body, Kirk hoped Christopher wasn't stuck in the body but powerless because he had learned what that felt like on Platonius and had hated it. (TOS novel: The Rings of Time)