The Pippala cave, also known as ‘Jarasandh ki Baithak’, is so named after King Jarasandh, a contemporary of Lord Krishna, as described in the ancient Hindu epic of Mahabharata. This Cave was believed to house the religious hermits of King Jarasandh, who came here from time to time for both spiritual healings and meditation.
A true wonder of nature, the cave has been carved out on Vaibhava Hill over the course of thousands of years by natural forces. Geometrically, it is a rectangular stone that appears to have acted as a watch tower for either the military installations posted there, or for the hot springs situated under the Vaibhava Hill.
The cave also attracts throngs of Buddhist followers, as it is believed to have been a centre of sanctity during the time of Lord Buddha. Pippala cave is also ideal for meditation, primarily due to its tranquility and peacefulness. The hot springs are a major tourist destination, with the water supposed to have medicinal properties capable of curing skin diseases.
Source
http://www.journeymart.com/de/india/bihar/rajgir/pippala-cave.aspx