"Open borders" is a bit of an oxymoron. Natural borders, such as rivers and mountains, have natural fords and passes which are more safe to navigate than other locations. The fords or passes are naturally open, when there is no statist intervention. States can take control of natural openings and fictional openings. Then crossers find different natural openings, or create artificial openings. The openings are quite distinct from a border. A border impairs or negatively influences passage, an opening enables or positively influences passage. Let there be natural borders and natural openings, without state interventions, without cultural definitions.
-- Kilgore Forelle