Vajranabha built a bathing tank at Syama Kunda to commemorate the place where Krishna killed Aristasura. When there is water in Syama Kunda this kunda cannot be seen. When Syama Kunda is empty, you can see a wall encircling a small deep kunda in the center of Syama Kunda. This kunda is called Vajranatha Kunda.
https://www.google.com/search?q=Vajranatha+Kunda
https://www.google.com/search?q=Vajranatha+Kunda
