Very good answers here. Just to add that the main route west from Bilbao along the north gets very busy but is pretty flat though there are some bits of uphill and downhill where the coastline has cliffs with little villages bolted onto them and the main road runs over the top with lanes down to the villages.
There are also some sandy bays to stop for a rest in the fresh sea breezes off the Bay of Biscay.
Northern Spain gets cool some days, hot other days, and sometimes it gets Great British Weather var Spanii......
Two or three brilliant days and then it's blowing a hooli and chuckin' it down.
Dress as for UK and take a brolly, three raincoats, towels. You know...the usual shopping gear for home.
If you stay too close to the coast you'll miss the lovely inland villages and the gorgeous Picos de Europa which is a dream of a place.
It's a lovely area to walk in and some of the rocks get unusual 'other world' shapes which you'll soon find piccies of via the search box ...Picos de Europa...select Images.
You'll be OK in a small car You'll see 2CV's there, Fiat 500s, and all sorts of small cars.
Just take it steady.
There are B&Bs, expensive hotels and guest houses, and camp sites, but it's like the Lake District for bookings...get booked up early or everywhere is full.
You could stay outside the Picos though and drive in. It isn't a huge area.
If the camp sites are full in any area you get to you'll usually be able to get a B&B in the little hostals in the towns with a bit of looking.
I've never been stuck for a bed in northern Spain at any time of the year but I'm always in the Picos out of season.
All the way along the north coast and inland there are lovely places to see. Aviles is a little gem when you're standing in the square in the old town and just taking it all in.....at night it's the local hotspot for drinks and parties.
The roads are fine, just like driving around towns and villages in the UK, some flat and some a bit hilly, but of course with a different character.
Spanish driving isn't cute and sweet though........take care.
Far west in Santiago you'll hear Celtic music because Galicia is a Celtic land where the local language is Gallego.
The food, as in Bilbao and all the Basque country,. is ........gorgeous.
Galicia and El Vasco get scouted for chefs by top restaurants all over Spain.
The Camino de Santiago is the oldest tourist trail in Europe and is now a popular walking route. There are high level and low level choices of route with some lovely scenery.
The Cathedral is magnificent and the whole city is worth visiting for the architecture and the food..
Go at night and see the Cathedral lit up. Sometimes the top disappears into the mist. The huge square and the buildings around it are a joy to be in....wonderful.
There are still some free refuges on the hills and in some of the towns for pilgrims walking (or driving) to the shrine of St James.
You're in for a great time.
Here's a bit about Bilbao and the north (under all the language bit) for somebody looking for a place to study..
https://answersrip.com/question/index?qid=20110325143400AAfxLB4 . . . . .