Aleph Stone Park is the simplest place to understand Natuna's appeal: pale granite boulders, blue-green water, and a shore that feels more like a wild version of Belitung than a standard beach stop. It is close enough to Ranai to visit without making a full day of it.
Come early or late for softer light on the rocks. Swimming depends on the sea state, but even a short wander over the boulders gives you one of the archipelago's strongest views.