If you occupy the fortress and the Fortress Battle ends, you'll have a brief window of time where you can teleport to a secret place inside the fortress.
In Siel's Western Fortress, you can teleport to a place called the Left Wing Chamber. Inside, there are supposed to be loads of treasures and relics the Balaur once looted.
I would like to see it for myself, but there are large numbers of Balaur guarding it. Could you kill them and help me investigate the [%dic:STR_DIC_W_IDAbRe_Low_Wciel_SZ_All]?
You're back! I've been waiting for you.
Did you teach the Balaur in [%dic:STR_DIC_W_IDAbRe_Low_Wciel_SZ_All] a lesson?
Great! Our getting ahold of these goods and resources will hurt both the Elyos and the Balaur.
Despite this victory, we must remain vigilant. The Balaur never rest, and neither can we.
For now, take this small token of my appreciation for your aid.
Defeat the Balaur at the [%dic:STR_DIC_W_IDAbRe_Low_Wciel_SZ_All]([%2]/40).
Click [%dic:STR_DIC_S_Quest_Get_Reward] in the Quest window or talk with [%dic:STR_DIC_N_Ab1_1131_TreasureGate_Da].
After occupying Siel's Western Fortress, go to the Left Wing Chamber and kill the Balaur there.
Srim asked you to enter the Left Wing Chamber after occupying the fortress and kill the Balaur there.
When you completed your task, he thanked you and gave you a reward.