Wadden — A Journey into the Hidden World of the Wadden Sea by Florian Huber. A close, evocative account of the Wadden Sea ecosystem: the tides, the mudflats, the birds, the seals, and the human communities that have lived beside it for centuries. Essential reading before a wadlopen walk.
The Dutch Landscape by Auke van der Woud. A cultural and historical account of how the Netherlands literally made itself — draining, diking, and engineering a country from water and mud. The flat Frisian coast makes sudden sense after reading this. More history than travel writing, but it reframes everything you see.
The Rings of Saturn by W.G. Sebald. Not about Friesland specifically — Sebald walks the coast of Suffolk — but the mood is exactly right: flat northern European light, solitary walking through an emptied landscape, history pressing in from all sides. If the Wadden coast makes you feel strangely melancholy and alive at the same time, Sebald has been there too.