Go to the Desert that's above Mauville City. There's a large rock near the bottom of the
desert that you can enter.

If you are playing Ruby/Sapphire, it will say "Right, right, down, down. Then, use
Strength."

If you are playing Emerald, it will say"Left, left, down, down. Then, use Rock Smash."

Do this and it should open a door. Go through the door to battle Regirock, who will be at
Lv. 40 and know Ancientpower, Curse, Superpower, and Rock Throw.

First go to the town in the water and go down the rapids on till u see a dark spot If ur
playin Emerald u need a Reliclanth first and a wailord last and a door will open if ur
playin ruby or sapphire it wailord first and Reliclanith last then u will go to another
door and it will say use dig use it and a earthquake will happen then do the steps love
pika said!