Path to Hellbound

Minimum Level: 78
Start Location: Wastelands 
Start NPC: Casian 
Rewards: Access to Hellbound

This quest starts with Elder Casian who is in the middle of the Wastelands. After you take the quest, he sends you to find Galate who is in Heine.

 
Galate is near the Gatekeeper and wants you to get a crystal from Casian. Go to Casian again and he will hand over the crystal that Galate asked you. Deliver the crystal and the quest will be completed.
Now as long as the Warpgate is powered up, you can access Hellbound.
 
*The quest is shared between main and subclass(es) so no need to do it more than once.