Sri Yantra is one of the most popular Yantras and it symbolically represents Mother Goddess Shakti. The story of the greatness of Sri Yantra is associated with Adi Shankaracharya and Shiva.
As per Hindu scriptures, once Adi Shankaracharya did penance on the Kailash. He performed various austerities and this pleased Shiva.
Shiva then appeared before Adi Shankara and granted him a boon. The holy saint did not wish anything for himself. Instead he asked for a permanent solution for finding peace and prosperity in the world.
Shiva then narrated about the greatness of Sri Yantra. He said that Mother Goddess resides in the Sri Yantra and therefore proper worship of it helps in attaining peace, prosperity and liberation.