The location of Blackfeather tower's treasure room was indeed very well hidden. If he had not obtained the map from the old Birdman, Tang Zhen would have really dug three feet into the ground to search for it.
After the completion of every tower, there would be a strange place. The strange thing about tower of black feather city was this maze-like underground passage. If one did not follow the correct route, they would fall into a closed dead end. They would not be able to find the exit and would be trapped to death.
The Blackfeather Birdman had actually used this passageway to build a treasure vault in the tower. It was quite original!
Tang Zhen fulfilled his promise and let the little Birdman go. The old Birdman didn't play any useless tricks and told Tang Zhen the true location of the treasure room.
It was a matter of life and death. These treasures were meaningless to the old Birdman. There was no need for him to risk his grandson's life.