Ischia is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about 30 km from the city of Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal, it measures approximately 10 km east to west and 7 km north to south and has about 34 kilometres of coastline and a surface area of 46.3 square kilometres . It is almost entirely mountainous, the highest peak being Mount Epomeo at 788 m. The island has a population of over 60,000 people. 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. The 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. For many of the inhabitants on the Italian-speaking island, German and English are second languages[citation needed]. This is due to the numerous German- and English-speaking tourists who visit the island each year