I think we drove over 1000 miles in our rented Nissan (nice car) from Lisbon airport, east into central Portugal, then north to the Douro Valley, then west to Porto, then down to Lisbon again. 12 days. The central plains are all agricultural (cork groves, olive groves, hayfields, huge pastures for sheep and cattle) then north (apples, chestnuts, peaches, cherries) until the endless hillside vineyards begin.
- The highways are excellent and well-marked. A pleasure. No traffic. Zero litter. Good truck lanes on hills.
- The rest stops are unprepossessing until you get inside. Really nice.
- Never saw anything but spotless bathrooms anywhere.
- Storks nesting all over, especially on powerline structures. Lots of swallows too. Harriers and Golden Eagles on hillsides.
- Off-highway, country roads. Good condition but curvy.
- You get tired of seeing hillside castles and fortifications. Wars since Roman times. We stayed in a few old fortified places.
- Everybody speaks at least some English, from grade school.
- Things generally are much less expensive than I expected.
- Meals are too large. Best thing I had there was a pile of sliced foie gras with a good drizzle of port wine reduction. Mrs. BD's favorite was a venison stew full of whole chestnuts. Yes, their pork and bacalao and oysters and fried cuttlefish too. Octopus always on menus too.
- The standard beer is SuperBock.
- Mapquest works perfectly. So does Alltrails for hiking. Interestingly, Merlin works for bird song. Those apps are life-changing for travelers.
- May is perfect. Maybe up to 70 day, 50s at night. Summer too hot.
- Plenty of Asian tourists. Few Moslems to be seen. We met a few people to connect with - an older Aussie guy smoking while his wife was in some shop, a couple from Newfoundland (really) but he grew up in Yonkers, and a serious boating couple from Connecticut who had done the Great Loop three times. Sheesh.
- If you ever imagined that Porto was a cute fishing village, think again. Streets crowded with tourists - Brits, Asians, Scandinavians, Germans, Canadians - all sorts. Not lots of Americans.
On our drive south from Porto to Obidos, we stopped in a seaside joint for grilled sardines. Nice. I do not know why they gave me a dark beer, but it was hydrating.
Mrs. BD is a world-class trip-planner and an adventurous one too:
The clash within civilizations by Heather Mac Donald 
Graduate Student Solves