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

In 1967 the complex was declared a Site of Cultural Interest in 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 tours in which various characters guide visitors through the fortress and the historic town centre, combining historical facts with references to legends associated with the place. The Torre de la Presó, a medieval structure located within the historic town centre, is a regular part of these guided tours.