Driving around Portugal and southern Spain

1) there are no border crossings. If you're driving along the border roads and don't pay attention to the signs, you may not know which country you're in.

2) Roads are very well marked, and getting lost is pretty difficult. Also, there aren't that many roads. I usually switch off my GPS for Spain/Portugal. Driving is a real pleasure.

3) You don't say what you have researched, but if you're on a road trip its almost a crime to miss:

In Portugal:
Monsaraz (across the lake you can see Mourao)
Estremoz
Elvas
Marvao
Monsanto
Sortelha

I also enjoyed
Castelo de Vide
Monchique
Cabo de Sao Vincente

In Spain:
Aracena
Jerez de los Caballeros
Zuheros
Montefrio
Cazorla

4) Parking in Seville and Granada is a major pain in the ass. I would make advance arrangements to make sure your hotel includes parking and reserves a spot for you. I have done this all times I've been there and never had any issues. Also, in Cordoba, there's a somewhat expensive hotel (by Spanish standards), I think it was called Maimonides, that has underground parking and its exactly 20 meters from the Mezquita, which is super convenient for that 8:30AM visit (the mosque is free in the morning and the atmosphere is superb with less people). You need to phone them when you get to Cordoba so they can open the old city gate for you (traffic is restricted there). Other than that there is parking in Passeo de la Victoria, both free and paid (cheap).

Also, I wouldn't drive around Lisbon at all its all rather compact, since I find that the hotels in Saldanha are better value than the old town ones I never have parking problems.

You will also meet "parking helpers" who "help" you park your car in a spot they have "reserved" for you. Give them 1-2 euros or risk having a scratched car.

G´day, whereabout do you plan travel and to cross the border in order to better give some ideas since imo your query is very ´broad´.
1. You mean formalities? None, it's EU.
2. Roads marked? Yes (of course). Maps: I used MAPAMAX, scale 1:400.000, you can buy one at a petrol station (Cepsa)
3. See above about narrowing down area.
4. No experience (I prefer not to hit cities and use public transport from adjacent 'places').
5. ?

My experience in Spain and Portugal is that roads outside of cities are rather well marked, but inside of the cities it is often very difficult. Streetnames are difficult to find and sometimes seem absent. We had a very difficult time to get out of Sevilla.
In the area of Spain, where I live, Galicia, the smaller roads are not properly marked and it is difficult to find your way around. However, I have the idea that it is easier in other parts of Spain.

Hey thanks, everyone, for your thoughts and guidance. I clearly wasn't thinking EU (borders), duh. I really appreciate your details, mredman, on parking and sights not to miss. And for the map suggestion, arizona. I think we'll try not to drive in any major cities -- great reminders.

Well, the borders are more or less like those state borders in the US. You'll find a blue sign on the road with the EU circle of stars with the country you're entering in written in.
It's a bit more complicated than that anyway. Inside the Schengen area (Portugal, Spain as well as almost all the EU countries), borders are usually not checked, so you do not even need to stop. Excepcionally though they can be checked. If that happens you must stop your car and cooperate with the police. There is no customs inside the EU except in some unusual places such as Gibraltar. There is a border control for passengers only (no customs) if you're travelling inside the EU but out of the Schengen zone (Ex: Travelling between France and the UK).

Regarding little exceptional places such as the tax heaven of Gibraltar, it's inside the EU but it's outside the customs union, which means there's a customs check point. If you want to go to Gibraltar while you're in Spain, it's always better to leave your rented car parked in the Spanish side of the border and enter Gibraltar on foot.

Avoid driving inside the big cities. Both Seville, and specially winding and hilly Lisbon can be really a pain. In the countryside of Southern Spain and Southern Portugal, driving is great: Usually flat, great weather, plenty of empty space outside the coastal areas and good freeways.

Thanks, joaop, for sharing your thoughts. Confirms my sense of big city driving generally - just not worth it.