Great walk, but don't stop when you reach Carmel River State Beach (continue walking to Mission Ranch and then the Carmel Mission). Walk, do. not. drive. All the beauty unfolds at a much slower pace than a drive-by affords.
Pass by historic houses, beautiful juxtapositions of plants against walls, birds and other wildwife, goofey dogs doing goofey dog-things that delight us all, and beautiful unparalleled naturescapes in all their magnificence. Sometimes slow is best; eyeballs need the extra time to process.
Our entire walk took us along this pleasant trail walk (catch it at "Scenic" trail in Carmel's beach area, it's a block "before" and south of the beach) and continue along the coastal walk past Carmel River State Beach through neighborhoods to the historic 1850's Mission Ranch, then to the Carmel Mission and end at the Mission Trail Nature Preserve leading back to Ocean Avenue and Mountain View. This is probably 4 miles in total.
This is our whole-hearted recommendation for a beautiful and enjoyable walk.