You can find The Nexus dungeon within Borean Tundra.
The coordinates are (27.1,26.2)
1. Commander Stoutbeard (Heroic Boss)
2. Grand Magus Telestra
/i Move away from player hit with Firebomb. Inflicts frost damage & stuns players. Pulls players towards her with Gravity Well, does shadow damage. At 50% boss splits into 3 mirror images. Can interrupt spells Critter, Time Stop, Scorch.
Heroic Differences: Arcane Attraction Will increase 1 players arcane damage taken for 10 sec.
4. Ormorok the Tree-Shaper
Heroic Differences: Summons Crystalline Tanglers, they root players.
/i Keep moving to avoid being slowed by Intense Cold. Avoid frontal cone Crystalfire Breath. Don’t stand behind boss to avoid Tail Sweep. Chains a player for 10 sec. At 25% boss enrages.
Heroic Differences: Crystallize holds all players for 10 sec.