Mythical roots

From Ramayana

The description of the beach paradises in Valmiki's epic Ramayana sounds like Unawatuna.
"a seashore dotted with thousands of trees, coconuts, and palms dominating, strings of houses and hermitages along the coastline, human beings and superior beings such asGandharvasSiddhas, and ascetics, living in them and countless bejewelled celestial nymphs thronging the shore, the coast intermittently visited by heavenly beings, Gods and demons.":
Unawatuna traces its roots to the great epic Ramayana. In the mythological epic, the monkey-warrior Hanuman was sent back to India to fetch the four medicinal herbs by Jambavan namely, mritasanjeevanivishalyakaranisuvarnakarani, and sandhani from the Himalayas in order to heal Lakshman who was wounded trying to save the abducted Princess Sita from the demon king Ravana. Hanuman failed to identify these herbs, so he lifted the entire mountain and carried it to the battlefield to try to save Lakshman, but in the process, a chunk of it "fell-down" in the location of the present day Unawatuna, the name of the village derives from "Una-watuna" meaning "fell down".
Currently, an edifice is being built in honour of Hanuman on the harbour end of Rumassala Hill by Japanese monks of the Mahayana sect of Buddhism near the Peace Pagoda that they built.

Alternate mythology

A banished Indian Prince was shipwrecked and the Goddess of Earth, Manimekala, taking pity created a rocky shelf for him to save his life and that subsequently he headed to Unawatuna. The Goddess of Chastity, Pattini, created a wall of fire to prevent him coming ashore, but being a person of some supreme power, he set in motion a tsunami with his foot to extinguish the fire and set foot on the shores of Unawatuna.
It is said that he lived in Unawatuna and helped the people in various ways. Over the years he has been venerated and worshiped, and the Kovil (or Devalaya) on the west end point of the bay which has a history of over a thousand years is believed to be the abode of this Devol deity.