Remarkable sacred grottoes are found on the coast, namely, the so-called Nyabi Kidul and Rongkob, and at Selarong, south-east of Jokjakarta.
From the 4th century onwards its grottoes were the dwellings of Christian hermits, amongst whom John of Lycopolis was the most celebrated.
On the north-west rock the caves known as the grottoes of Pan and Apollo were cleared out; these consist of a slight high-arched indentation immediately to the east of the Clepsydra and a double and somewhat deeper cavern a little farther to the east.
Various volcanic rocks are the predominant formations, but beds of limestone also occur, giving rise to numerous stalactite grottoes all over the island.
The Mithraic temples of Roman times were artificial grottoes (spelaea) wholly or partially underground, in imitation of the original selcuded mountain caverns of Asia.
The southern part of the province belongs to the Karst region, and here are situated the famous cascades and grottoes of Sankt Kanzian, where the river Reka begins its subterranean course.
Was obtained, and also of commercial traffic from the distant west in the shape of records in Indian, Kharoshti and Brahmi scripts and an unknown script resembling Aramaic. The sacred grottoes known as the Halls of the Thousand Buddhas, south-east of Tung-hwang, were visited, with their frescoes and cave temples, and a large number of documents and examples of early Chinese art were recovered.