Siegesmith Stouthandle in Wintergrasp wants you to retrieve 10 Eternal Embers from Horde players at the Cauldron of Flames.
<name>! About time you showed up. While we may have lost the last battle, we should prepare for the next! Travel to the Cauldron of Flames in southeastern Wintergrasp and retrieve several eternal embers.
The embers are mixed in with coal to fuel the Demolisher and Siege Engines.
Oh, and if you happen to see some of the Horde in the Cauldron, don't hesitate to slay them and take their embers. We must prevent them from holding the keep!