A short boat ride from Kayangan Lake, Twin Lagoon is two inland salt lakes connected by a small underwater tunnel. Boats anchor at the first lagoon; to reach the second you either duck through the tunnel underwater (about a metre below the surface, doable in goggles) or, at low tide, scramble over a small wooden ladder over the rock arch.
The water is layered — a warmer freshwater layer floats on a cooler salt one, and you can feel the temperature shift as you swim down through it. The cliffs are home to swiftlets and the occasional macaque.