Santa Cruz da Graciosa is the capital of Graciosa — the most low-lying and serene of the Azores islands, nicknamed "White Island" for its light-coloured volcanic rock and whitewashed houses. The extraordinary Furna do Enxofre, a thermal cave with a sulphurous lake inside a lava bubble, is one of the most remarkable natural phenomena in the archipelago, and the island's traditional windmills are among the most picturesque in Portugal.