Grenen is the northern tip of Denmark, a blade of sand beyond Skagen, and it is not in the same place it was a century ago. Currents dredge sediment along the Jutland coast and drop about a million cubic metres of it here every year, so the spit keeps growing north-east. It has added close to a kilometre in a hundred years. The country's official northernmost point moves with it. At the end of that sand two seas meet at an angle: the Skagerrak on one side, the Kattegat on the other, waves running in from left and right and slapping together on the last bar at your feet. The seam is visible because the two differ before they blend — lighter, brackish water coming out of the Baltic against saltier, denser water from the North Sea.
You walk the last two kilometres, with the sea closing in from both sides until only a strip is left. Nobody swims at the end of it. The currents where the seas cross are lethal, and the signs say so in four languages. From the top of the striped Grey Lighthouse you finally see the shape of it: a thin curving blade splitting the water into two colours. Freighters and tankers pass close to the point on their way between the North Sea and the Baltic, one of the busiest approaches in Europe. In April and May the tip becomes the best raptor lookout in northern Europe. Eagles, red kites, buzzards and cranes stack up at the end of the land and circle over your head until the wind serves, then strike out for Sweden; a southeasterly fills the sky over the sand, a southwesterly sends them somewhere else. At sunrise and through the long Nordic evening the low sun turns the wet sand to a mirror. The walk out to the tip is longer than it was in the oldest photographs of it, and the sand has not stopped arriving.