Nagatoro is a small town on the Arakawa River, at the point where the water leaves the Chichibu mountains and cuts through a long stretch of flat, banded rock. The riverbed here is made of crystalline schist, a pale green stone laid down in broad stepped terraces, known as Iwadatami, or rock tatami, because it looks like a floor of giant mats. Geologists have studied the formation for well over a century, and it is among the most celebrated rock exposures in Japan.
The best way to see it is by water. Open wooden boats, steered by boatmen with long poles, carry passengers through the rapids in a trip that lasts about half an hour, and it is a fun and slightly wet experience in summer. In winter the boats run with covers and heaters. A footbridge and a path along the bank give good views, and the autumn colours of the surrounding hills are lovely. The town has a number of shops selling shaved ice, noodles and souvenirs, and the main street has an old-fashioned atmosphere.
At about 140 metres above sea level, the town sits in a gentle valley, and the roads leading out of it climb into the hills in all directions. They are mostly narrow and winding, with some tight bends and occasional rough patches, and they are popular with riders on weekends. Traffic can build up in the town at peak times, especially on sunny Sundays, so early morning is the best time. Near the river you will find parking for motorcycles at several spots.
The nearest large town is Yorii, about seven kilometres away, with petrol and supermarkets, and there are petrol stations in Nagatoro itself. A bowl of soba or a plate of the local miso potato dumplings makes an easy lunch. Shaved ice with syrup, made from natural ice, is also a local speciality in summer.
Walk down to the rocks, take off your gloves and watch the water. It is a lovely, quiet place to stop.