Successfully complete the game. Once done, wait three weeks. After the third week you will get a visit from Mr. Karnab. He informs you that new passageways have opened in the ruins that you have. Go to adventure and press Right or Left to switch from normal adventure to Adventure +. Adventure + is much harder then normal adventure. All the wild monsters are "S" rank, and the ruins have many levels (about 10). Of course, the items are much better in Adventure +.