This achievement is earned for finding the eigth secret and can be found on Checkpoint 34
It can also be found in this video, with a text description of its location below
[7:01] - Secret 8 of 13
This takes place during the "20 man puzzle". You'll need to gather a few followers from the bottom and middle left) and then go to the bottom right. Use the followers to help you gain access to the very left by using the large minecraft and rope to find new caged followers. Upon releasing them, head back to the elevator, and on your way back you will notice a patched up wall, which can be destroyed using the new followers. Go inside, down the ladder, take the torch, and use it to defend yourself against the wolves and make your way to the left of the cave.