I live in Spain too (Near Pamplona)!
Anyway, that appears to be a ladder snake (
Rhinechis scalaris). These snakes have teeth, but no venom, so although they are a very intimidating snake species, it is completely harmless. I have caught a lot of these snakes and although they have a painful bite, there is no venom so a little blood is all it is. As a general rule of thumb, if you see a big snake in Spain, it is harmless, it is the smaller ones you have to be careful of. Spain is home to 3-5 (depending on who you ask the differentiation of species is different...) species of vipers, all of which have potentially dangerous bites. All of these vipers are pretty rare, so I wouldn't worry about encountering them very often (in my 5+ years of searching for snakes I have encountered 3 vipers). With that said, there is one species of snake called the montpellier snake or the culebra bastarda (
Malpolon monspessulanus) Which is venomous and is (again depending on who you ask) europes largest snake growing to be 2m+, and is mildly venomous, however this is nothing more than some swelling and bruising if bitten.
This is probably a lot more of information than you were looking for... but I figure too much is better than not enough... Hope this helps!
Ladder snake:
https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAD
Venomous viper:
https://www.google.com/imgres?imgurl...MygDegUIARC8AQ
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