The Tottori Sand Dunes are sixteen kilometres of wind-built sand ridges falling into the Sea of Japan on the coast of Tottori prefecture, in western Japan, the country's most famous dune field, up to fifty metres high, kept bare only because volunteers weed the invading grass by hand, and they are climbed, boarded down, paraglided from and walked after snow. The sand came down the Sendai river from the granite mountains over a hundred thousand years and was piled by the onshore wind into three ridges, and after the war the pines planted to hold the sand and the grass that followed began to close over them, so the prefecture and its volunteers pull the grass every year to keep the dunes as dunes; the middle ridge, Uma-no-Se, the Horse's Back, is a wall of sand 47 metres high with no path up it from below, climbed in a slog to the crest, and on the sheltered side of each ridge the loose sand slides downhill until it stops at the steepest angle dry sand can hold, leaving a slope that is ridden on a board. The winds that move the sand blow from autumn to early spring, corrugating the whole field into ripples, while summer is the calm season.
Since 2009 it has been illegal to mark the dunes with any letter or figure larger than ten square metres, and the prefecture fines for it. The onshore wind makes the main ridge a tandem paragliding launch, with the whole coastline opening below, and the Sand Museum next to the dunes is the only indoor sand-sculpture museum in the world, rebuilt around a different country every year. A Sea of Japan cold snap buries the gold ridges under snow, and the same wind blows sand back over the white in dark streaks, so a fully white dune field shows only a handful of days each winter. Tottori is a desert on a wet coast, and it is kept a desert by hand.