Castro Castle is a fortress of Arab origin situated in the Sierra de Espadán, in the municipality of Alfondeguilla (Castellón). It stands at 787 metres altitude on a rocky spur that dominates the surroundings of the Sierra de Espadán Natural Park, one of the most extensive protected natural spaces in the Valencian Community.

Although the defensive construction is of Arab workmanship, the site has precedents of Roman occupation, with evidence of a watchtower on the same hill before the Islamic building. This strategic use of a point of visual control over the territory is a constant throughout its history.

Following the Christian conquest, the castle became integrated into the feudal defensive network of the area, although it gradually lost its military function. At present, ruins of the walled enclosure and some sections of wall are preserved, visible from the exterior and accessible on foot via marked paths.

The most common access is from the Alfondeguilla town centre via the Collado de la Mina or the Barranco de l'Horteta, medium to high difficulty routes that combine a visit to the castle with other heritage elements such as the Castro Ice House and the area known as l'Arquet. The complete circular route is approximately 10.9 kilometres.

The panoramic views from the summit encompass much of the Plana Baixa region and the interior reliefs of Espadán, which reinforces the interest of the visit from both a heritage and landscape perspective. The castle is catalogued with the code CS-CAS-044 in the Castillosnet register.