Other sites, such as Allahabad, have been the hub of hundreds of tantric practices, and therefore within the radius of a dozen miles or so almost any kind of tantric sadhana will be fruitful. And because thousands of devout practitioners and millions of faithful pilgrims visit Allahabad every year, they perpetuate the concentration of spiritual energy there. As a result this city is called tirtha raja (the lord of all shrines).
