To reach this zone, you will need to go through the instance The Oratorium of Thyr in Solusek's Eye. Once inside you must defeat Flame Lord Thyr for the back door leading to Nagafen's Lair to open up.
To take the elevator at ( -316, -595, 187 ) /waypoint -316, -595, 187 up from level 7 to 6, RIGHT click on icon to left of door and click up.
ATTENTION : You need to Hail him (default Key is "H" in order to engage him!
During the fight you'll be exiled to a hanging barred cage, fight the flame spirits that are burning you, and then send your merc (or another player if you're in a group) to kill Flame Lord Thyr (You can use ranged weapons too. Once defeated, you ll be freed and can enter Solusek's Eye
Other Details are covered in the article for quest To Speak as a Dragon.