Bad Lands Cave
Enderic can be found wandering outside Chlera to the east. For a price - $20,000 gold - he will tell you the secret to entering the "Lost Dungeon City of Amnon Vre" in after you kill 50 ettins for him. If you change your mind and don't want to kill ettins, he'll keep your gold. But he's an honest thief and when you return, he will remember that you've already paid him.
The entrance to the Badlands Cave and Lost Dungeon City of Amnon Vre is at 2291,2782,0. Once inside, the switch is located through a secret wall at 2462,2982,1. Pull it and run back out south, west and then south again through the gates which will now be unlocked for a matter of seconds.