The black rock by the side of Isigili.
It was there that Godhika SN.i.120f. and Vakkali SN.iii.124 committed suicide.
It was a lonely spot, and we are told that when monks came from afar to Rājagaha they would ask Dabba Mallaputta to find them lodgings there because they wished to see evidence of Dabba’s iddhi-powers. Vin.ii.76 Vin.iii.159
The Buddha is mentioned SN.i.194 as having stayed at Kāḷasilā with a great company of monks. On one such occasion the Buddha is said to have given Ānanda an opportunity of asking him to continue to live for a whole aeon. But Ānanda failed to do so. DN.ii.116
In the Cūḷadukkhakkhandha Sutta, MN.i.92 it is said that Kāḷasilā was also the residence of some Nigaṇṭhas.