Now backtrack all the way back to Troia castle. The very first thing you have to do is revisiting Edward. After a long conversation, you'll obtain Bardsong augment. 

Augment:

• Give Bardsong to Tellah. (I know it sounds weird but you have to give Tellah 2 augments in total; Bardsong is kinda useless anyway).

Next, go to #4 the main hall and talk to Epopts to gain access to underground prison for more treasures.

Remaining treasures in Troia castle:

• Hi-Potion (x2)
• Remedy (x2)
• Ether (x2)
• Dry Ether (x2)
• Elixir
• Silver Apple
• Echo Herbs (x2)
• Great Bow
• Ice Arrows
• Fire Arrows
• 50,000 gil
• 5,000 gil
• Lightning Arrows