Well go to Argent Vanguard, in Icecrown, and use the Siege Towers.

HeHe ;D

Can any of you all believe this joke Blizzard put in, by having the Reckoning Bomb in the game as a special attack for a Siege Tower?

Anyway, the quest is very interesting. So destroy 100 Undead, and as you build up power, you can then Unleash your most powerful attack (The Reckoning Bomb )

I had to fight one horde over a tower, but that was nothing.

I did die after the quest, cause one of those stupid Elite Dragons one shotted me, as I was getting off the Siege Tower. > :-\ :'(
But lease we Get to use Flying Mounts as a ghost, running back to body. :-*