Parque Regional de Sierra… in detail
The website http://turismo.alhamademurcia.es details some of the marked walking routes in the sierra. Wikiloc (www.wikiloc.com) also has many routes waypointed.
Mountain-bikers should check out www.espubike.com, which details a four-stage 146km route around the park, starting at El Berro. It's been designed to be accessible for all abilities.