Krishna dug Krishna Kund when Radha insisted that he purify himself by bathing in all the holy rivers after he had killed the Aristasura demon who was in the form of a bull. So rather than going to all the sacred rivers, he simply dug his heel into the earth and called the presiding deities of the various holy rivers of India to merge their waters into the pool.
After bathing, He explained to Radharani and the gopis that the bull was actually a demon, so they should also take a purifying bath to rid themselves of the sin of siding with a demon. Radharani became upset and decided she could also make a kund or lake. Thus, she and the gopis broke their bangles and dug a hole, but it remained dry to Krishna’s amusement. However, by using water from the nearby Manasi Ganga lake and the waters from the presiding deities of the holy rivers who appeared, Her kund also filled up. Thus, these kunds are very special to pilgrims who visit. It is said that anyone who bathes here will get the perfection of Krishna prema, which is far beyond mere liberation from material existence. It is said that Radha Kund is the liquid form of Radharani’s ecstatic love for Krishna. And since Radha Kund is Lord Krishna’s favorite bathing place, anyone who bathes in Radha Kund gets the mercy of Lord Krishna and will attain Krishna prema, ecstatic love for Lord Krishna. Similarly, Radharani also said that anyone who bathes in Shyama Kund will get Her special favor. Therefore, Radha Kund is difficult to attain.