The secret Goblin temple is located in the north part of the Goblin cave. The stairs leading to it are guarded by 2 goblin guards, who will only allow you to pass if you are in goblin form after drinking a goblin potion. The temple is heavily involved in the Land of the Goblins quest, as well as the Hopespear's Will miniquest that follows it. The temple was originally built overground, on the Plain of Mud, but it sank underground.