Enter the Castle and walk up the stairs, where you will meet Sphinxara. There is nothing to do but attack. After this battle, you will be able to unlock one command. Choose magic, so that you will have the ability to heal your party members.
Now, head through the doors at the top of the stairs and walk across the floor until the chandelier falls down. Head forwards and open the hatch in the floor. Climb down the spiral staircase where you will meet Tri-Point. This monster is weak against Fire and Ice, so use some magic to finish him off. In the far right corner there is an Aura Draw Point. (Come back to this later, after you have unlocked the Draw command).
Walk back up the spiral staircase and head to the door to the left. Follow the corridor to the end. Exit the door on the right to return to the lobby. Make your way back up to the top of the stairs and head to the right to find another door. Head through this door and down the stairs to the bottom and then enter the door to the North to find a picture gallery with lots of paintings on the walls. Examine the paintings on the first floor, then go up the stairs and examine the paintings on the second floor. Go back down and observe the large painting on the left hand side. You will now have to guess the name of the ainting. It is VIVIDARIUM, INTERVILIUM, VIATOR. Next you will battle Trauma who will appear after you guess the apinting's name. For more information on how to kill Trauma, click here.
Head through the door to the North to find some steps which lead to a small dungeon. Head down these stairs to the bottom and enter the cell on the left. The door will slam shut. Check the corpse in the corner of the room and you will find the key in his hand. Take it, but then the Red Giant will battle you. This enemy is weak against Gravity based magic and very strong against physical attacks. Hit him with Demi spells until they are only dealing about 100HPs of damage, then kill him with physical attacks.
Use the key to open the locked cell door. Head back up the stairs and find another passage on the left at the top of the next staircase. There is a Cura Draw Point. Continue along the crumbling passage and there is a Save Point. Use the small elevator to go down to the ground floor. Head South along the passage into another small room. Climb the stairs on the left. Follow the path around and enter the passage on the right-hand side. You will now find yourself back in the castle lobby so go to the foot of the stairs and step into the switch point to change over to the other party. Take this new party through the door on the left and follow the corridor around to the room where the chandelier falls. Stand in the centre of the switch point here and you will press a hidden switch. Change back to your main party and climb the stairs to the top. Walk across the chandelier which will now not fall, and enter the door opposite to find another monster waiting for you. This is Krysta.
Head back to the castle lobby after the battle, and walk down the stairs to the bottom. Enter the door on the left. Make your way around to the room underneath the chandelier. Head North through the door to a small courtyard, then head over to the left to a Slow Draw Point. Search the fountain for the Treasure Vault Key. Climb the stairs on the right and you will reach an old bridge. Press the triangle button while moving forwards to walk across and pick up the key to the Armoury Room. Head back down to the courtyard fountain and return to the lobby. Climb the stairs to the top and take the right path. Go to the dungeon and use the Armoury Key to open the locked door. Go inside and you will see a Vysage at the back of the room. Run up to it and fight it. After this battle, Gargantua will appear. Watch out for Status effects.
After the battle search the suits of armour and there will be an Ultima Draw Point to be found. Stock some then exit the dungeon and go up the stairs on the left. Head down the crumbling corridor to where the Save Point is, then go down to the ground floor in the elevator. In the next passage, search along the left wall to find a hidden door to the Treasury. Inside there are four coffins which will open and close at random when you inspect any of them. Keep checking out the coffins, until you get all four open at the same time. Now Catoblepas will appear.
After the battle, stock some spells from the Holy Draw Point from the coffin in the middle of the room. Go back to the courtyard fountain and head through the doors on the far side. Climb the stairs on the right and walk across the bridge. Enter the door ahead of you and climb the spiral path to the top of the tower. Eventually, you will see a bell. Press X to jump onto it, then jump off it when it swings to the other side. Go through the hole in the wall on the right and there will be Tiamat.
After the battle, go back to where the bell is, and jump onto it. Jump off when it swings to the other side, so that you will be back on the spiral path. Climb to the top. There is a Stop Draw Point. Now go South and walk across the clock face. Go down the ladder. Walk down the path and save your game. Go through the door for the final battle. For more help on the Final Battle, click here.
With thanks to the Strategy Guide I used.