Father Serra had all the Indians from the San Diego mission start at the bottom of California and build a road all the way up to the top of California connecting all the missions together. This was long hard work. Many Indians died of hunger and thirst. The soldiers that were watching over them so they wouldn't run away refused to give them their food and drinks unless they built three miles of the road. By the time this road was done a Spanish Ambassador had taken over because Father Serra died. They gave the road the name " El Camino Real ", meaning " The Royal Road ".
Today most people use the highway that runs roughly along El Camino Real. The old road is still there but it isn't neat and it's falling apart. But if you're looking for adventure it might be fun to try and travel it from one mission to another on El Camino Real.