The ridge above the Porta Westfalica is where the Wiehengebirge, a long thin line of hills running east to west, comes to an abrupt end at the Weser river. Seen on a map, the range looks like a ruled line suddenly cut by a knife. In fact it is a belt of Jurassic limestone and sandstone, tilted and eroded over millions of years, and the river found its way through at the weakest point. That geology is the reason the road along the crest is so quietly satisfying: it follows a sharp edge, with steep wooded slopes falling away to the north and gentler land to the south.
The ridge also carries a heavier history. Late in the Second World War, the hills near Hausberge and Barkhausen were used to build underground production halls in old mine workings, using forced labour from a satellite camp of the Neuengamme concentration camp. The tunnels are still there, and a small memorial in the area records what happened. It is an uncomfortable fact to find in such a calm woodland, and it deserves a minute of quiet before you ride on.
Today the road is a pleasant, winding country route. It rises through beech and oak in a series of gentle bends, passes a television tower and a couple of old inns, and comes out at clearings with views across the plain toward Minden, whose cathedral and flat roofs lie to the north. The Mittelland Canal, one of Germany's great waterways, crosses the Weser near Minden in an aqueduct, a surprisingly good thing to watch from above if a barge is passing. The surface is mostly smooth, although tree roots lift the verge in places, and some corners are blind. On warm weekends there are plenty of walkers and cyclists, so the best time is a weekday morning.
Services are down in the valley rather than on the ridge. Porta Westfalica has fuel stations and supermarkets, and nearby Minden has a bigger choice, with a handsome old river town centre and a long record as a Prussian fortress and Weser port. Bad Oeynhausen, about nine kilometres away, is a spa town with a large park. Fill up before climbing, and bring water.