The Sealed Chamber is located on Route 134, between Pacifidlog Town and Slateport City. It opens the entrance to the Regis' caves. The language on the rocks are Braille. After opening the doors to the Golem Trio's caves, they can be accessible.
First get a Wailord, Relicanth, and a Pokémon that knows Dig. You have to maneuver your way through the currents of Route 134 to find a square-shaped patch of Dive-able spot.
Dive down and follow the path to a rock with Braille.
Read it and a door will open.
Enter the doorway, then surface.
Now put Relicanth in the front of your party and Wailord in the back or vice versa.
Once that is done, go to the back of the room and read the middle text on the far wall.
Then use Dig. You should hear a rumbling, which means the doors to the Regis are open.