The reminder room was a facility aboard a fake spacecraft in the bunker used by Operation Golden Age. There, the people who Sir Charles Grover had duped into believing they were colonists watched footage about the perils life on Earth that had resulted from pollution, war and overcrowding. Mark told Sarah Jane Smith "we all come in here from time to time to be reminded of the purposes of our mission".
After Sarah claimed she had been brought to the spacecraft against her will, Ruth decided that she had to be "re-educated". Sarah was locked in the room while the footage played.
Ruth told Mark and Adam that if she remained unchanged afterwards, they would have to destroy her. Sarah forced her way past Mark when he opened the door and locked him in. She returned and let him out so that she could prove to him that the spacecraft was fake. (TV: Invasion of the Dinosaurs)