You can find the Halls of Lightning dungeon within Ulduar, The Storm Peaks.
The coordinates are (44.8,21.7)
1. General Bjarngrim
/i When out of combat will charge electrical energy to increase damage. Kill adds first. Boss has Battle, Berserker & Defensive Stances (mainly deal physical damage). Run from Whirlwind.
/i Deals a lot of nature damage & explodes knocking players back. At 50% breaks into Sparks of Ionar that follow players dealing high damage that stacks, run away from them down the stairs to avoid.
Heroic Differences: Arc Lightning shocks a player inflicting nature damage & causes them to shock others.