It is hard to point at a spot, because there is no spot: the sea retreats twice a day, leaving miles of glistening mud, and then returns, often faster than you expect. The Wadden Sea is a UNESCO site shared by the Netherlands, Germany and Denmark, and it is the largest unbroken system of intertidal sand and mud flats in the world.
Its importance lies in what lives there. The mud is thick with worms, shellfish and tiny crustaceans, which feed vast numbers of migrating birds, including knots, oystercatchers and spoonbills. Common and grey seals rest on the sandbanks, and the whole system acts as a nursery for North Sea fish. You can walk on the flats with a guide, a tradition called wadlopen, from villages like Pieterburen, but this is a practice to be done only with an experienced guide, since the tide and fog can trap the careless.
For a rider, the interesting parts are the roads along the dykes. The Frisian coast is flat, open and breezy, with long straight sections along the sea wall, sheep on the grassy banks, and a sky that seems far bigger than elsewhere in Europe. Wind is the main character: a headwind from the north-west can make the day hard work, while a tailwind is a joy. Weather changes quickly, so keep rain gear handy. Spring and early autumn bring migrating birds, and summer evenings are long and golden.
The ferry from Holwerd runs to Ameland, where Nes and Hollum have a small supply of shops, fuel and restaurants, but on the mainland the larger towns of Dokkum and Leeuwarden offer more choice. Franeker, home of the Eisinga Planetarium, is the other direction on this ride. Built in a living room in the eighteenth century by a wool comber, Eise Eisinga, it is the world's oldest working planetarium, with a ceiling that models the planets. A cup of strong coffee with a slice of Frisian sugar bread makes a fine afterwards.