Luon Grotto is situated on Bo Hon Island, 14km south of Bai Chay Beach, In front of the grotto is Con Rua Islet and the Sky Gate is on the right. Here the cliffs stretch vertically out of the pure blue and smooth water.
At the water-level, an arched entrance leads to the grotto, just at the base of the island. Passing through the pretty entrance, you come across a tranquil round lake, surrounded by luxuriant trees .This is an enclosed group of islands. It connects with the sea via a 4-meter-wide, 100-meter-long, and 3-meter-high mouth. Inside the grotto, the 1-km2 brackish lake is surrounded by mountains. On the cliff one still find traces of fossils of fresh-water snails, which prove that men used to live there and this must have been a deep valley then.