Metropolis City High Security Prison is a prison in the Metropolis Zone and is presumbly the most secure facility in the whole of Mobius. The prison was chosen to be the new home of Grimer once Doctor Robotnik was defeated after the events of Robotnik Reigns Supreme. For some time, Grimer was presumably a standard prisoner like the rest of the criminals detained there. However, he was soon able to completely overthrow the Governor and took over the prison. In order to retain secrecy, no criminals were released in this time. With the freedom of the prison, Grimer set up a new laboratory in the grounds which would allow him to research the whereabouts of his master. In this time, he also constructed a new model of the Metallix Mark 3 and kidnapped Sonic the Hedgehog. With the hedgehog in his possession, he managed to extract Sonic's knowledge of Robotnik's disappearance. He then forced the Governor to lie to Sonic about the current ownership of the prison.
Later, Grimer would perform another attack from inside the prison. From his workshop, Grimer was able to remotely hack into the Kintobor Computer, making it believe that a Badnik attack was occurring in the Metropolis Zone. In reality, it was just a plot to get Sonic out of the Control Centre and to face the Kintobor Badnik. Sonic eventually figured out how to defeat it, heading home and turning off the Kintobor Computer. In the time that the system was down and before Porker Lewis could install new protective measures, Grimer had installed a surveillance system into Kintobor's sensors.
After Grimer left the prison to meet up with Nack the Weasel and continue the search for Robotnik, life went back to normal for the inmates. Some time later, a SMART Missile sent by The Trickster broke into the High Security Prison as one of the riddles to be solved by Sonic. The phrase was "The villains you face, end up in this place!" Sonic instantly solved it and the missle cut open a hole in one of the outerly walls. To Sonic's surprise, Mr Fry appeared (despite there being no reason for him to be there or to not be Proctor Speckle) but Sonic swiftly defeated him.