When you approach the crystal, you will be attacked by a Land Turtle. It has a lot of HP, but the Antarctic Winds you picked up on B2 can each deal more than half of its maximum HP in damage. After defeating the boss, you will earn your first five new Jobs. All of them are better than the Onion Knight Job your characters are currently using, though you'll lack equipment and Spells to make the use of most of them.
Once you're done here, stepping onto the magic circle behind the crystal will result in the party being transported outside.
Once you're done here, stepping onto the magic circle behind the crystal will result in the party being transported outside.