On a bike trip in northern Spain this year, I was suddenly surrounded by 3 plainclothes officers in Santander inside a small regional train station. I was waiting for the track number to be posted for the narrow gauge train I was taking to get out of town to avoid its extensive industrial suburbs. One of the officers showed me his law enforcement ID and asked to see my "documento de identidad". In Spain and many other countries, it's legal for law enforcement officials to stop anyone at anytime and demand to see their papers, which you're supposed to carry on you at all times. I handed my passport over to the Spanish officer. He read through it and looked for my entrance stamp to the European Union. He then phoned in my information to someone who apparently ran it through a computer and confirmed that I there legally. He asked me a few questions about where I was biking and handed my passport back.