Cycling on highways is a total no-go here. I've never heard of it happening, and I'd expect the police to be called whenever someone sees it.

You're right on the narrow streets and low speeds. That is a much bigger cultural / civil-engineering thing. It makes me wonder how cycling infrastructure is done in Rotterdam. It's city centre needed to be completely rebuild after WW2. The result is regarded by some as ugly or 'american'. Perhaps this has affected cycling, or perhaps that was taken into account in the rebuild.