We just spent 4 days in Portugal after disembarking in Lisbon. I found great rental car rates (under $100 for 4 days), and we planned to spend a couple of days in Lisbon and the same in Porto. I have driven in many different countries, both left and right side, and am comfortable with a stick shift. Nothing prepared me for driving in Portugal. Whoever designed their roadway system should be drawn and quartered. There was never, not once, an occasion where we traveled more than a couple of miles from point A to point B that did not include numerous round-abouts, U-turns, and at least a dozen different roads. Sometimes they didn't seem to be roads at all - more like alleyways and through parking lots. We used two different GPS systems, often simultaneously, and still made wrong turns quite frequently (and a wrong turn could easily add another half dozen turns and ten minutes to your journey). Parking near tourist attractions was difficult, if not impossible to find, and often involved parallel parking on the street in a space only a few feet longer than our car. Parking decks were rare. Don't even think about driving to Sintra unless you just want to drive through it without stopping.
I consider myself a pretty safe driver with no accidents since I was a teenager (a long time ago), but I literally came within inches of hitting two cars. I was an absolute basket case after every trip. The tolls will also eat you alive. We had close to $100 in tolls during our four days there which pretty much balanced out the cheap rental car rates.
We've been home for a week, and I'm still suffering from PTSD from this trip.