According to my in-depth internet research, a causeway is a raised track enabling one to travel by various means over wet areas, many inaccessible at low tide. These include railways, roads and of course my favourite, walkable paths.
If you study Ordnance Survey maps there are many to be found around our shoreline. Take one to be transported to deserted islands, ruined buildings and giant's stepping stones. Sturdy boots or wellies and a good knowledge of the tides are de rigueur for exploring these sometimes hidden tracks. I love 'em!