How do you make the gym doors unlock in cinnabar island? - Answers

I have only done this in Pokemon Yellow, but this should be the same in Fire Red and Leaf Green. On Cinnibar Island there is a building that suffered a fire and is now in ruins. Inside that building is a total maze of rubble where one can find a scientist's journal revealing that Mew was actually under research there and had "given birth" to Mewtwo. In this building will also be a key that opens the gym doors. In Crystal, Gold, or Silver the gym has been relocated to the Seafoam Islands due to a volcanic eruption. These islands are in the sea to the right of Cinnibar Island. In a cave on the only one of the islands you can go to you will find the leader, Blake. Hope this was helpful.