Cueva de las Estrellas Nature · Castellar de la Frontera, Campo de Gibraltar, Cádiz Image of Castellar de la Frontera, not of the place itself. A cave with prehistoric rock paintings located within the municipal term of Castellar de la Frontera, within the Los Alcornocales Natural Park; it was declared a Bien de Interés Cultural in 2017. declarada BIC en 2017 Photo: Luis Rogelio HM (CC BY-SA 2.0) What to see and do in Castellar de la Frontera