Go to Pacifidlog Town and ride the current to Route 134. If you followed it correctly, you should come to a dive spot. Go down and continue underwater to the white mound. Read the inscription and resurface. You should be in the Sealed Chamber. Go to the back of the chamber, read the inscription, and use Dig; the wall should open. Go to the back of the next chamber and arrange your party so that Wailord is the party leader and Relicanth is in last position; when you read the chamber in back and your party is arranged this way, a tremor should occur. After that, leave the Sealed Chamber.
Regirock: Desert on Route 111. Go to the southern part of the Desert and go in the monolith. Read the inscription and walk two paces left and two paces down and use Rock Smash.
Regice: Route 105. Locate the sandbar with vegetation and bank to the left. Go up the water path on the left and enter the monolith. Read the inscription and run a full lap along the perimeter of the chamber.
Registeel: Route 120. Go to the pond at the southern part of the route and go into the tall grass at the staircase. You should come to a monolith. Go in and use Flash in the centre of the chamber.