Onda Castle is a Muslim fortification from the 10th century built over the remains of an ancient Roman settlement. Known as the 'castle of 300 towers' due to its considerable size, it occupies an unparalleled strategic position on a hill from which it commands views of both the town of Onda and the La Plana Baixa region and the Sierra de Espadán. In 1250 it was transferred to the Order of the Temple and subsequently in 1319 it passed to the Order of Montesa.

In 1967 the complex was declared a Heritage Asset with the category of Historic-Artistic Complex, a recognition that also extends to the entire old town of Onda.

The castle currently houses a museum and can be visited throughout the year. The local authority also organises theatrical guided tours in which various characters guide visitors through the castle grounds and historic town centre, combining historical facts with references to legends associated with the place. The Torre de la Presó, a medieval structure situated within the historic town centre, is a regular feature of these guided tours.