From Coimbra to Castelo Branco with a stop on Pampilhosa da Serra, just pure fun with full power on tight corners. A "must" if you want to try really good roads in Portugal.
It starts at Torres Vedras with good straight roads, then it goes wild once you turn left on the junction until Alenquer. There, stop for some photos by the river, over the bridge and then a few hundred meters further with Alenquer village scattered on the hill. Lots of green and forest, great tarmac, fun corners.
Alternative path from Alverca to Bucelas