Pokémon Ruby Tips

How to unlock the 8th gym door.
Find the hidden cavern, by using dive to the south of Mossdeep. Search the ocean floor, until you find a little cave with a sumbarine in it, then use dive again to appear in the cavern. Beat everybody in it, then make your way through the cavern.When you come across it, beat Team Magma leader. From there, you will be assigned to go to Sootopolis City, to the cave of origin, go in there, and find and catch Groudon. Then the gym door will be unlocked, so you can go on a battle with Sootopolis City's gym leader, Wallace.