Ischia is an island off the coast of Naples in the Bay of Naples. Other islands in the Bay of Naples include Capri and Procida. Capri is the more famous and upscale of the islands. Capri has been the go-to place for the rich and famous since the 1930s. Both Capri and Ischia are about 17 miles from the city of Naples and the trip to each takes about 40 minutes by fast ferry.
Ischia is not a large island - about 27 square miles. This compares to 4 square miles for Capri and as a comparison Martha's Vineyard is about 100 square miles. Ischia has taller mountains in the interior with the highest point being 2600 feet. By comparison, Capri has as it highest point 1900 feet and Martha's Vineyard is 300 feet.
Ischia has hundreds of thermal vents due to the fact that it was formed as a result of a volcano. The Greeks were the first to note the therapeutic value of the baths with their abundance of minerals. There are many spas on the island and some areas where you just sit in the sea and pick a spot where the sea does not get too hot.