Castillo de Castro is a fortress of Arab origin located in the Sierra de Espadán, in the municipal area of Alfondeguilla (Castellón). It stands at 787 metres above sea level on a rocky spur that overlooks the surroundings of the Parque Natural de la Sierra de Espadán, one of the most extensive protected natural areas in the Valencian Community.

The defensive construction is of Arab workmanship, but the site has antecedents of Roman occupation: a watchtower has been documented on the same hill prior to the Islamic building. The use of this point of visual control over the territory is a constant throughout its history.

Following the Christian conquest, the castle became part of the feudal defensive network of the area, although it gradually lost its military function. Today, ruins of the walled enclosure and some sections of wall survive, visible from the outside and accessible on foot via signposted paths.

The most common access starts from the village of Alfondeguilla, via the Collado de la Mina or the Barranco de l'Horteta, routes of medium-high difficulty that combine a visit to the castle with other heritage features, such as the Nevera de Castro and the area known as l'Arquet. The complete circular route is around 10.9 kilometres.

From the summit, the views encompass much of the comarca of the Plana Baixa and the inland reliefs of Espadán. The castle is catalogued under the code CS-CAS-044 in the Castillosnet register.