In Pokémon Ruby, after going to Mt. Pyre and getting the Red Orb, you have to go to Lilycove City and enter Team Magma's Hideout.
Battle and Get Items
In the entrance of the hideout, you see a Grunt running around. He has two level 32 Poochyenas. After the battle, go north to reach the next room.
Step on the lower white circle to find a Max Elixir. Step on the circle again to go back to the first room, then step on the upper white circle. Afterward, go through the north door.
Walk east and you find a grunt who has a level 33 Zubat. (You can avoid fighting her if you walk as far to the left from her as you can on your way to the stairs.) Go up the stairs past the grunt. Then step on the white circle.
Go east and you will find two grunts. The girl has a level 31 Poochyena and two level 31 Numels. The guy has a level 32 Numel and a level 32 Zubat. Go southwest from those grunts and step on the white circle, then step on the other white circle in the next room.
There are many teleporters here. First, step on the upper-left one. Then step on the middle one. Then step on the right one. Finally, step on the bottom-right one. You will end up in a room with four items on the left side of the room. Two of these are Electrodes, one is a Nugget, and one is a Master Ball. This is the only chance to get these items, so be sure to get them now.
When you are done in the room where you got the Master Ball, step on the white circle. Then step on the middle circle, then step on the left circle, and finally step on the circle in the top middle of the room. In the next room, step on the other white circle to return to the large area with the two grunts on the east side. Go to the far right of the room and step on the white circle there.
Go to the left. There is a grunt there who has two level 30 Poochyenas, a level 30 Zubat, and a level 30 Numel. Then go through the northwest door.
Go to the right to find a white circle. Step on it and go down to get a Nest Ball. Then go back up and step on the white circle.
To the south, there is a grunt who has a level 33 Numel. Southwest of there, you find another white circle. Step on it.
Go southwest and you find Magma Admin Tabitha. He has a level 32 Numel, level 32 Mightyena, and level 32 Camerupt.
After you defeat Tabitha, go to the left and then up to find another white circle. It takes you back to the entrance of the hideout. Leave the hideout.
When you go outside, you discover that you can now Surf east to Route 124.