Nagatoro

The Arakawa cuts through a band of crystalline schist at Nagatoro, and the river has scoured the rock into a broad flat shelf along the bank known as Iwadatami, the rock tatami - flat enough to walk out on and step-jointed like matting. The rock is a metamorphic sequence formed at depth and brought to the surface, and the outcrop is significant enough that it has been studied since the nineteenth century and is sometimes called the birthplace of Japanese geology. Traditional flat-bottomed boats, poled by boatmen who read the water rather than steer with engines, run passengers down two sections of rapids in about twenty minutes each; in winter they are enclosed and heated instead. The valley colours in early November and the Chichibu Railway runs a steam locomotive along the line on some days.

What you actually see

• Iwadatami - a flat shelf of crystalline schist scoured by the river.
• Poled boats - traditional flat-bottomed craft running two sets of rapids.
• A geology site - an outcrop studied since the nineteenth century.
• The steam train - a locomotive on the Chichibu line on scheduled days.

When to go

April to November; early November for colour. Half a day.

Honest expectations

Boats do not run in high water after rain. Autumn weekends are congested and queues for boats are long. Trips are short - twenty minutes per section. Winter boats are covered, which limits the experience.

Nearby

Hitsujiyama Park and its shibazakura are south at Chichibu.