The underwater tunnel turns through about 90 degrees, so you descend into total darkness for a few seconds. Once you complete the turn, you can start to make out the emerald-green light coming from deep within the island. As you exit the tunnel and enter the lagoon, the water glows a deep emerald green and it’s rather like being inside a big, green volcano. There’s a large sandy beach to relax on, that’s open to the sky inside the cave.