Ok, first things first�levelling! You need to be at least level 35 to go through the Cave OK. I was well over that before I went in, and I still had a bit of trouble. Anyway. When you enter, use the necklace to open the Sealed Cave. Take the rope down to the next platform, and be careful, because if you try and open the door beneath you, it will turn into a TrapDoor. These are infuriating.
TrapDoor:
OK, it�s not really a boss, but it deserves a strategy. It will immediately cast Target on a party member, then use Dmension to kill them. Deal damage quickly, and then you can defeat it. It could, however, turn in to a different monster, which can also be annoying. Revive characters immediately. Bio is quite effective. If you are fast enough, you may only lose 1 person.
In the room is a Kotetsu and an Ether1. Leave and get the chest on the left containing a Bestiary. Continue left and up the rope to a door. You can sense it can�t you? Another TrapDoor. When you beat it, continue. Get the chest on the left for a HiPotion and the one on the right for an Ether1. In the room on the left is�nothing. In the room on the right is also nothing. Waste of HP and space. Continue through the door on the right.
Take the rope to the bottom and get the StarVeil, then continue up and along the bridge on the right. Get the chest containing a Life before continuing upwards. The first room contains nothing, the second room contains the Light Sword, the third contains an Elixir, a Fuma and a StarVeil, the fourth contains nothing, the fifth contains a save point. Save and heal. The final room contains another Kotetsu and a Ninja Helmet. When ready, head onwards. Fight another TrapDoor, and enter the next room. Get the chest containing an Ether1 and continue. There�s a Life and a HiPotion, and ignore the door on the left, since there�s nothing inside. Continue through the south passage. Go behind the next door to get a MuteBell, and take the rope in the middle of the path. Check the room on the right for an Ether2 and an X-Potion. When done, go down the stairs on the left. Save and heal.
Go through the south passage and circle round. Head up and through the stairs. Go along the bridge and into the Crystal room. Take the Crystal. If you lost some HP on the way here, use items or Cecil to heal before heading back out. As you leave, the walls begin to close in.
EvilWall:
This can be tough. Just use Bio or Titan for Rydia, Jump with Kain, Berserk Cecil, and have Edge throw anything he can or attack. Rosa heals all the way. EvilWall slowly moves towards your party, attacking along the way. When he reaches you, he uses an instant kill attack. Make sure you kill him before he does so. He also tries to petrify your party, so keep healing. If you levelled well enough, you shouldn�t have a problem, but don�t let your guard down.
Aah, now that that�s done, use Exit. Wait�it doesn�t work�Ok, try Warp. No. Oh well, just leave normally, no more TrapDoors, so it should be a breeze. As you leave, the screen turns dark�Golbez! Kain returns to his command and steals the Crystal from you! Leave, save, and return to the Dwarven Castle.