Pahiyangala Caves lie in Yatagampitiya, a remote village about 5 km away from Bulathsinhala (40km along Piliyandala-Horana road), in the Kalutara District. Excavations have proved that these caves were inhabited by prehistoric cave men some 37,000 years ago. This cave is supposed to be the largest natural rock in Asia and this is also known to be the oldest pre-historic human settlement in Asia.
The cave lies 400 feet above sea level. At its entrance, the cave is 175 feet high and over 200 feet long. It is believed that 3,000 people can be easily accommodated in this cave. The natural tunnels running into the caves are now blocked and not accessible for safety reasons. The cave has been divided into four sections of which the left side cave is the largest. There is a deep pit dug out by the Archaeological Department for an excavation. In this pit archaeologists discovered five human skulls which were identified as 37,000 years old by carbon dating in USA. Some weapons made of stone and animal bones were also recovered during the excavation. It has been found that these were used to kill monkey, deer, porcupine and other animals. The cave men are also believed to have consumed acavus, a species of edible snail, and wild breadfruit.
Biologically, this cave dweller known as Pahiyangala Manawakaya (Pahiyangala Man) had a short vertebral structure, wide jaw bones , a large palette and big grinding teeth.
The name of the cave is derived from the name of the Chinese Mahayana Buddhist priest " Fa- Hsien" who visited the cave in the 5th century. This Chinese scholar-bhikkhu was a tireless wanderer in strange lands. It is learnt that Fa-Hsien sailed with two friends Bhadantachariya and Buddhaghosa. The latter was a Pali scholar, commentator and author of Vissuddhi Magga (a classic manual of the Buddhist doctrine and meditation), and they sailed from the mouth of the Hooghli river in Calcutta to Sri Lanka in 411 CE.

Fa- Hsien obtained a copy of the Disciplines and Long Agamas when he visited Anuradhapura and from there he was determined to climb the Sacred Mountain "Sri Pada" and pay homage at the Buddha's foot print. His pilgrimage to Sri Pada lasted several months because the route to the peak was through Bulathsinghala, Kalawana, Nivitigala, Ratnapura and Gileemale. On his journey, it is believed that he had lived several months in the Pahiyangala cave and a vessel which was supposed to have used by him was discovered during the excavations.
Later this cave has been converted into a Buddhist temple by a priest called Porogama. According to legend Ven. Porogama Thero had used a 6 foot Yakula which was similar to an iron crowbar. This iron crowbar is so heavy that even six people find it difficult to carry it. He is said to have used this to push aside the debris and soil that obstructed the entrance to the cave. He was also said to have been able to level the ground. The Yakula is now tied to the feet of the reclining 40 foot Buddha statue. Ven. Porogama Thero also constructed two colossal door frames for the Vihara which can be seen at the entrance.