The Door Closes (閉じられた異次元世界 Tojirareta Ijigen Sekai, lit. "The Other Dimension is Sealed Off") is the four hundred ninety-second chapter of the Dragon Ball manga.
Goku says Majin Buu's ki has vanished, and Supreme Kai suddenly notices it as well. But they also can't feel the youngster's ki either. Old Kai says they've just been fighting in the alternate dimension of Time. Goku doesn't understand what he means, but then realizes it must be the Hyperbolic Time Chamber. He wonders why they've been fighting in there, and Old Kai explains that the Namekian led Majin Buu in there for some reason. Goku compliments what an awesome Supreme Kai the old guy is, and Supreme Kai admits that he is relatively useless now.
Gotenks thinks of what a great job he's done, but Piccolo exclaims that Majin Buu will revive himself. They need to burn up all of his flesh. Piccolo helps him out, and after a while they're finished, as Gotenks stomps on the last piece. Piccolo thinks this is great, it's finally over. However, there's a sudden gush of wind up into the sky and Majin Buu begins collecting above them. Boo reforms, and Gotenks realizes frying him didn't do any good after all, noting that Buu looks thoroughly pissed. Piccolo thinks they should have just wiped out Buu with their ki instead of burning him, and then to be sure, they should have destroyed the entrance to this room so that Buu would be sealed away in this world in a different dimension.
Piccolo asks Gotenks if he can do that Super Ghost Kamikaze Attack again, or maybe some other great technique. Gotenks thinks he still has plenty left, but he wants to scare Piccolo a bit, for fun. Gotenks dramatically exclaims it's all over, he has no more power for other attacks. Buu suddenly grabs Gotenks' leg with his forelock, and starts slamming Gotenks around. Gotenks, hanging upside down, calls Buu "baldy", which prompts him to punch Gotenks and send him flying. Gotenks is really angry now, and finally prepares to use his best technique, but… Piccolo suddenly destroys the entrance to the Hyperbolic Time Chamber.
Piccolo tells Buu it's all over, because he's destroyed the only entrance between the two worlds. There’s no way out. Piccolo tells Buu that even if he kills them, he'll spend eternity alone in this empty world. Buu thinks of his beloved candy, and Piccolo says there's no candy here. Gotenks yells at Piccolo for having done that, since he still had his best technique left. Piccolo yells back at him, bringing up what he said about maxing out, and Gotenks says that it was a joke. Piccolo says this is no time for that, and the two of them call each other idiots. Buu, who hasn't been paying any attention to the two, suddenly starts fiercely screaming. His enraged screams are so loud that a hole opens up in front of him and The Lookout is visible through it.