In town, walking can be a good way to get around Ischia specially in high season when there is lot of traffic on the streets. You can enjoy the amazing town centers with their stores, bars, restaurants. A car can be a problem in the towns as there is few parking spaces and you can only park in public and private areas. You can always take a taxi or a microtaxi. Keep in mind that you need to negotiate the charge before the trip starts.

Many travelers prefer to rent a bike and that is a good choice if you plan to go to other towns or plan to cruise the countryside. Be careful about motorbikes, however, as traffic is heavy during peak seasons and Ischitano drivers are as aggressive as Roman drivers.

The best way to go around is by bus. The bus system is extensive and covers all the towns of the island, having the main terminal in the city of Ischia Porto. This can be found at the bus stop located about two blocks to the right of the ferry dock (standing with your back to the sea), and one street inland from the harbor.The service is frequent and you won't be stranded at any part of the island. And, it is cheap! The single trip is 1.20 Euros and you can use that same ticket for 90 minutes on any other route. You can also get a  giornaliero (24 hour) bus pass for 4 euros.

The numbered buses all show their destination on the front, so it is easy to get anywhere. Also, the CD bus goes clockwise around the island all day, and the CS bus goes counter-clockwise. (Remember D = destra, S = sinistra.) For the castle (Castello Aragonese), you want Ischia Ponte, about 10 minutes clockwise from Ischia Porto. Forio is about 20 minutes counter-clockwise (or take the #7 bus) from Porto.

Or, rent a driver with car.