you beat eliet 4 and complete pokedex and go up again and a girl will talk to the lady you get in.
THIS UP TOP IS WRONG!!!!!!!!
you have to get a wailord and a relithcanth(probibly spelled wrong^_^) and go through the maze on routs 133/134 STAY IN THE MIDDLE!!!!!!!!! if done correctly you will find a small diveing patch. dive. and when you come to a big block look for the dot, dive up and u are in the sealed chamber. u must have tm28dig go to the wall straight ahead and go to the center of the wall. use dig, another chamber will open and put relicanth in 1st and wailord in 6th then go to the center of the far wall , press a and it will start to shake. then a message will apear and u can now go to routs 111, 105 and120 and catch them NOTE:very hard to catch, needs lots of timer and ultra balls.