You say NW Spain, so don't know if you'll be arriving via the Santander or Bilbao ferries or driving down through France. Assuming you'll be heading SE from Santander/Bilbao, or S via Bayonne for that matter, a great place to visit is an area I nicknamed ‘the dustbowl’ when we used to run Landy Rally (Alps and Spanish Pyrenees Charity Drive). The dustbowl is a national park in Navarra called “Parc Natural Bardenas Reales”
located southeast of Pamplona, just north of Tudela; it’s truly amazing. Boasting designated off-road tracks though a semi-arid desert, it comes complete with vultures, eagles, etc. … the works! Switch to Earth in Google to see what I mean. There is a lake there which is worth investigating, plus the famous 'termite mound' - my nickname again! There is a photo of it at the bottom of the Google Maps Earth page. When you view it in the flesh, you'll see there are four layers of rock at it's peak ... this is the original level of the ground, the rest has eroded away over centuries to form this impressive pyramid.
The best entrance to the park is heading east from a town called Arguedas (approx. 12km north of Tudela on the NA 134), then as you hit the gravel keep heading east until you head north and complete an entire loop of the area.
Of course you can find info about the area via the internet, but the map you’ll need for “Parc Natural Bardenas Reales” (with off-road routes clearly marked) is Michelin Regional 574 Catalunya/Aragon/Andorra 1/400 000 1cm: 4km. Only £3.99 - £4.99 off the net - mapsman is where go, good price and reliable: www.mapsman.com
Wiki is as good a place as any to start researching it - http://en.wikipedia.org/wiki/Bardenas_Reales
- the place is magical.
Also, depending how long you are there, an excellent campsite can be found in Ejea de los Caballeros – again east of Arguedas and Tudela:-
Camping Complejo Bolaso
c/o Rafael Avellana
Crta. Gallur-Sanguesa, km.46.1
CP. 50600 (Ejea de los Caballeros)
Tel. 976 66 80 43
GPS N: 42º10’41’’ W: 1º11’05‘’ www.bolaso.es
Really helpful owner (Rafael) and his son who speaks very good English, plus a great restaurant. Say you know Tom McGuigan of Landy Rally, they always associate me with Landy Rally (in case you weren't aware, Landy Rally was a 4x4 charity drive though the Alps and Pyrenees held from 2007 - 20011).
The other place to visit if you have time is the tax-haven of Andorra, where a you can buy branded vodka/whisky for 29 euros – for a massive 4½ litre bottle (that was a few years ago, but still it's probably only 35 euros at today's prices). Of course, being off-roaders, the only way to enter/exit the country is via the “Smuggler’s Route”. Again very easy once you know. It’s a route we tend to keep to ourselves, so please don’t go broadcasting it on the net (as some idiots have done in the past). PM me for precise directions.