For Portugal, I recommend RN2:

Estrada Nacional 2
The National Road 2 (EN2/N2) is nicknamed the Route 66 of Portugal. It’s a very exciting and scenic journey in the heart of the country, taking you from Chaves in the North to Faro in the South.

The road is totally asphalted. Completed in 1950’s, it’s the longest continuous road in the country crossing 4 mountain ranges, 11 rivers and 29 municipalities. The journey offers an exhilarating driving experience, with superb views. An incredible journey, an unforgettable experience. The journey is a wonderful way to slowly travel through the country and experience Portugal's diverse culture and landscapes through stunning landscapes, unique villages, irresistible river beaches, unforgettable heritage and unique gastronomy.
The road encompasses miles of stunning views. It has been named one of the “best places to go in 2019” by American travel guide publisher Frommer’s. The experience of using this road is very impressive. The road is 738km long. It starts at the city of Chaves, in the northern part of the country, close to the border with Spain deep in the rough landscape of Trás os Montes. It runs south through the centre of Portugal, and ends in the city of Faro, just short of the Atlantic Ocean where the visitor is faced by the azure sea of the Algarve.