Sierra Espuna (closest mountain range to Murcia) has great bike trails, although none of it is waymarked but there are guidebooks written in English.
When I was out there the English folk that ran the hotel in Gebas (say Hebath and spit the H out as in loch) provided a guiding service it's called Hotel La Mariposa.
Or stay up in the village El Berro the (Spanish but English speaking, ask for Andres) guys that run the camping Sierra Espuna are proper bikers (as opposed to the hard tail fluoro lycra mincing down fireroads that most of the locals do) and might take you out if you ask nicely.
I would say tho – the Sierra Espuna starts at sea level and climbs to just over 1600 metres yes thats metres so has correspondingly tough climbs and technical descents, most folk seem to ride Orange Patriots for reasons that will become obvious if you go there and ride with them !
Ah the memories !! Missing the Mille Coin (74,000 corners) climb already !