Five mountains were situated around Magadha, the capital of Jarāsandha (Jarasandha). Ṛṣigiri (Rishigiri) is one of these five mountains.

Mahābhārata (Kinjawadekar)(2.21.2)
Mahābhārata Vols. 1-43 (Siddhāntabāgīśa)

According to scholars, Ṛṣigiri was located near Ratnāgiri (Ratnagiri).

(The Indian Encyclopaedia, p. 4434)