***(There have been several reports of this achievement not popping for some people after the requirements have been met. You could follow the steps outlined in the comments to start a new save and get it. Be willing to lose your progress before you do this though.)***
Complete the Goblin King's Hall Encounters.
There are 5 Goblin King related cards. You get the first one automatically by finishing a game after the release of the Title Update 2. They are easy to recognize because of the purple banner and icon in the top right hand corner of the card.
Quick Guide to Goblin King's Hall Cards:
Goblin King I. Listen. Accept Goblin.
The Maiden. Request Hair.
Goblin King II. You will lose your gold and enter a maze of traps. Pick up gold on the ground along your way. When you reach the end, you will have to enter another maze if you do not have enough gold. It took me 3 maze runs to accumulate enough gold.
Goblin King III. Enter a maze of traps where you have to break down a wall of boxes along the way to open a chest before completing the maze.
Goblin King IV. Ask about capital. Find another Vault. Enter a maze similar to previous one, but you will have a goblin in the center throwing grenades at you while you are going through the maze. If there is a chest in this maze, you will need to grab that as well.
*If this solution helped you in some way, please vote positively. If you think it needs improvement, please let me know how in a private message or by leaving a comment.*