Once you're in Sundletan,there'll be an earthquake, and Maxim will start running around frantically

Explore the town, and you'll hear rumors that a giant catfish living inside the Lake Cave is causing the earthquakes. Buy yourself some armor and weapons and go to the cave in the middle of the lake

Just in case you dont know how to enter, go here.

Now, do this to get the Insect Crush, one of the most useful weapons for this part of the game.

Stay on the lookout for hidden passages like this one in future dungeons

In the bottom part of the room where there's a hidden passage, there's a line up of 8 enemies you have to defeat to get to the speedy ring. This will be a breeze if you equiped the Insect crush and are about level 6.

Eventually you'll meet the master catfish, the source of the earthquakes. He's not hard, just heal yourself when needed, and if you've managed to get the eagle rock from the eagle monsters, use its IP attack. Go back to the village and you'll learn that a young lady had been looking for Maxim and she went inside the cave. Go back to the cave and into the room where there's a locked door leading to the Insect Crush

Save her and she'll then join your party.

Don't buy her more than the basics. Get her strong, spark and some armor. Her attack power is low, but she's a useful magician.

Head back to Sundleton to save and rest and then head north to the small shrine to Alunze kingdom.

To go to Alunze,you need to go north. First, go find capsule monster foomy in the woods just south past the small shrine on the other side of the mountains.

Refer to this for info on capsule monsters.