Within Parque Natural Sierra de Grazalema, is the Zona de Reserva, for which special permits are required:
The Spanish fir forest and other areas in the Reserve can only be visited at certain times of the year, and visitor numbers are limited, so you are advised to get information in advance.
According to the Spanish Wikipedia article, the Centro de Visitantes (visitor centre) in El Bosque serves for obtaining authorisation to access de Zona de Reserva:
Centro de Visitantes de El Bosque. C/Fco. García Lorca s/n. 11670, El Bosque. Tfno.: 956709733. Este centro realiza las funciones de central para la obtención de autorización de acceso a la Zona de Reserva.
And according to Sierra de Grazalema: Complete Guidebook to the Natural Park, reservations must be made between 1 and 30 days in advance and are limited to 20 people per day. The guidebook lists a telephone number (which is different from the one on Wikipedia or the park website) that I have not tried to phone yet, but in my experience the English language knowledge of visitor centre employees can be very limited (and my Spanish is poor).
How do I apply for a permit to visit the Zona de Reserva in the Parque Natural Sierra de Grazalema?