Ischia is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about 30 kilometres (19 miles) from the city of Naples. It is the largest of the Phlegrean Islands. Ischia is the name of the main comune of the island. The other comuni of the island are Barano d'Ischia, Casamicciola Terme, Forio, Lacco Ameno, and Serrara Fontana. Ischia's main industry is tourism, centering on thermal spas that cater mostly to European (especially German) and Asian tourists eager to enjoy the fruits of the island's natural volcanic activity, its hot springs, and its volcanic mud.