The Aragonese Castle of Baia is a medieval fortress located on the small island of Ischia in the Gulf of Naples, Italy. The castle was built in 1480 by Alfonso of Aragon, the King of Naples, on a rocky outcrop overlooking the bay of Baia.

The castle was designed by the Spanish architect Giovan Giacomo Palearo Fratino, who used the latest military technology of the time to create an impregnable fortress. It features a drawbridge, a moat, and high walls with towers, as well as a chapel, a prison, and a governor's residence.

Over the centuries, the castle was used as a military garrison and a prison, and was also the residence of various noble families. It was damaged by an earthquake in 1805 and abandoned, but was later restored and opened to the public as a museum.

Today, the Aragonese Castle of Baia is one of the most popular tourist attractions on Ischia, offering stunning views of the surrounding sea and coastline. Visitors can explore the castle's many rooms and corridors, admire its ancient architecture and artifacts, and learn about the fascinating history of this important stronghold. The castle is accessible via a causeway from the nearby town of Ischia Ponte, or by boat from the port of Ischia.