Halls like this one at Karle and the ones at Ellora and Ajanta are carved out of hillsides. All the interior elements are integral to the cave -- meaning that they are not built separately and set into the cave, but entirely carved out of the living rock. The hall leads back to a stupa.
overview notes of the period from the Dept. of Architecture at UC Berkeley
descriptive entry at Chaitya.com
entry at Great Buildings Online
