As an alterntive to the Vía Augusta from Cádiz (or Algeciras), it is apparently possible to walk from La Línea de la Concepción to Seville, taking about 234km.
It sounds like a great add-on to the Vía de la Plata. The route goes through or past San Roque, Jimena de la Frontera, part of the
Sierra de Grazelema natural park, Ronda (one of my favourite places on earth), vulture colonies at Peñón de Zaframagón, joining the Augusta at Utrera, a day from Seville, with 30-odd km on the
Vía Verde de la Sierra, and four churches of Santiago en route.
I wonder if any forum members have walked it - the main advantage (for me) over the Vía Augusta is that it's clearly a
lot less flat. The
Asociación Gaditana Jacobea has produced a useful looking guide to the route, and also posted the stages on wikiloc. I'm committed to the Mozárabe from Almería this year, but the Serrana/Plata is looking likely for 2017