The Mines of Kaderak - Act 3 Story Quest
The Mines of Kaderak is a two part quest with this consisting of the first part. You'll start this quest immediately following your completion of The Kalrathian Rebellion. In order to reach the Mines of Kaderak entrance you'll want to take the Teleporter to the Southern Desert of Kaderak. This is a new location that just became available to you when you accepted this quest.
All you need to do for this quest is to destroy the four statues which you can find surrounding the entrance to the Mines of Kaderak. They're impossible to miss as you'll run into them shortly after teleporting to this area. Right click the statues and they'll get smashed easily. It's a rather simple and straight forward quest, however there is some optional exploring that you can do in the nearby area.
I'd recommend scouting out the areas to the east, west and north completely prior to going into the Mines of Kaderak. If you go far enough north you'll even find a Teleporter - along with a nearby elevator that's used in the Finala's Contempt Side Quest. When you're ready to complete this quest and move onto the Mines of Kaderak you'll want to destroy all 4 statues then head down the elevator and go inside.
Once you enter the Mines of Kaderak this quest will complete and the next one, The Mines of Kaderak (Part 2) will begin.