To get to Regirock, the Sealed Chamber's puzzle must be completed. After this has happened, the ruins can be accessed.
To open the door in Pokémon Ruby and Sapphire, once in the lobby area, at the Braille inscription, the player must go two steps right, then two steps down, and then use Strength. The Braille reads: "Right, right, down, down. Then, use Strength."
To open the door in Emerald, the player must instead go two steps left, then two steps down, and then use Rock Smash. The Braille reads: "Left, left, down, down. Then, use Rock Smash."
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.