A few years ago, my partner and I were staying on Pontevedra and decided on a day trip to Tuy by bus, which lies directly on the Spanish/Portuguese border. Whilst we were there, and admiring the Gustav Eiffel built bridge across the Minho, I suggested we walk to Valença do Minho - a very pleasant walled city in Portugal - about 2km away - across the pedestrian deck. My other half was a bit uneasy as she didn’t have a passport or ID with her, but we weren’t stopped in either direction. However, the following day we took a train from Vigo to Porto, and when we got to Valença, there was a full passport inspection on the train - Schengen notwithstanding. Seems we were just lucky the day before.
We had a very unpleasant experience going to Germany recently - on the Luxembourgish border, the CFL run bus was detained for 25 minutes whilst they painstakingly checked everyone’s passport or ID card, and photographed them. About 30% of the passengers had no ID on them at all, and…the border police did nothing at all. It was all for show. Elections next year and being crappy to foreigners wins votes. I suspect they (the Grenzpolizei) didn’t want to complete the (no doubt voluminous) paperwork.
France will be joining in this idiocy in a week’s time.