Isola d'Ischia is the largest of the islands in the Gulf. It is a collection of craters and ancient lava flows, but there are difficult to identify under the lush semi-tropical vegetation. There are numerous hot water springs, many of them with bathing establishments, indicating that there is still subterranean activity. From antiquity it has been famed for its hot mineral springs strict conditions are laid down for bathing in them.
Although not as well known, the island's beauty rivals that of Capri: steep high mountains rising to Mount Epomeo are covered in lush semi-tropical vegetation. Today it is much visited by tourists and also has a considerable permanent foreign population. There are several harbours around the island and although the main harbour, Porto d'Ischia, is mostly taken up with ferries and yachts permanently moored there, the island can be explored from the other harbours.