Carcaboso can be a bit confusing to find your way around, the village is a knot of narrow streets. From where the camino arrives, head left along the main road for most services. Return to the camino where you left it or otherwise find your way to the Iglesia de Santiago, there are three Roman milarios there from the emperors Trajan and his adoptive son Adrian. Trajan is best remembered as a great promoter of civic projects such as roads.
The way from Carcaboso to Ventaquemada is a return to nature with a few options along the way. The first turn to pay attention to is less than a kilometer out of town where your natural tendency is to always keep on a straight path; the camino turns right at a sign for Finca Bombay (an adventure sports company, in case you are inclined to rent an ebike). Not far beyond that turn is a split, and here both options are perfectly viable. To the left is somewhat shorter, and to the right is a trail marked H1 along the more historic path.
The two options rejoin and continue through the countryside to Ventaquemada.