Goa Rangko, also referred to as Gua Rangko, is a limestone cave located a short drive and boat ride from Labuan Bajo in Flores, Indonesia. With the entry of sunlight, the natural pool inside it brightens into brilliant blue, which makes it one of the region's most unusual attractions. Visitors can have a swim in the mineral-rich water, explore the interior of the cave, and bask in a quiet coastal setting. The light in the cave is best during the afternoon. Reaching it requires a short boat ride from a nearby harbor. Many travelers combine it with the Pasir Timbul sandbar nearby for an easy half-day adventure.