The Upanishads and the third eye.
The Upanishads are a set of philosophical texts. They constitute the theoretical basis of the Hindu religion.
*In the Upanishads, the human being is a city with 10 doors.
*The two eyes, the two nostrils, the two ears, the mouth, the urethra and the anus are the nine doors. They lead to the world of the senses.
*The tenth door is the Third Eye, which leads to the inner world.