It heads north through the wooded Sierra Morena and passes over the Puerto de las Marismas.

North of Mérida the road crosses the Sierra de San Pedro to the town and world heritage site of Cáceres.

18 km north where the road will meet the reservoir Embalse del Esla de Ricobayo is under construction as of October 2013.

Entering Asturias, the roads re-converge 36 km south of the next major city Oviedo.

The A-66 finally ends 13 km north of Oviedo at a junction with the Autovía A-8 near Gijón on the Atlantic Coast.