Watarase Keikoku Railway Third Kanbai Tunnel

One bore, two building eras

The Watarase Keikoku Railway Third Kanbai Tunnel is a single-track railway tunnel of 1912 at Shimokanbai in Omama, Midori City, Gunma Prefecture, and it was listed as a Registered Tangible Cultural Property in 2009. The original bore measures 45 metres. Its lining is turned entirely in brick, four courses thick, with cut stone used only for the portal, and the horseshoe section curves gently from end to end.

In 1937 a reinforced concrete structure 15 metres long was joined to the southern end. It is a rigid frame of posts and beams, boxy where the older work is arched. Midori City puts the original bore at 44.81 metres and the addition at 15.4 metres, for 60.21 metres in all. The year of construction and the contractor's name are incised into the concrete of the newer section, so the extension carries its own dated record.

A refuge niche for track crews was cut in 1974.

Three tunnels for a stretch called the Seven Bends

Between Kirihara and Shimokanbai the Watarase River has cut cliffs that come right down to the rails. The old copper road through here was known as Nanamagari, the Seven Bends, and the Ashio Railway dealt with it by driving three tunnels. The Watarase Keikoku Railway Third Kanbai Tunnel is the northernmost of them, only about 90 metres from the Second Kanbai Tunnel, with the Fukasawa Bridge some 3,100 metres further upstream.

Registration came on 2 November 2009, with public notice on the 19th of the same month. The listing covered station buildings, bridges and tunnels along the whole line from Kiryu to Mato, 38 structures in total. No other Japanese railway had ever had an entire line listed across two prefectures. The criterion applied was contribution to the historic landscape of the country, and in 2016 the same group of structures was recognised as a Civil Engineering Heritage by the Japan Society of Civil Engineers.

Fifteen metres where the darkness changes texture

What rewards attention in the Watarase Keikoku Railway Third Kanbai Tunnel is how the wall changes character during the few seconds it takes to pass through. Brickwork is close jointed and unevenly fired, so it catches the light in patches. The concrete section is flat and seamless and throws light back differently. Notice where one gives way to the other and you have found the seam between 1912 and 1937.

Riding towards Kiryu from Kamikanbai Station, the portal comes into view about two and a half minutes after departure. From the Third Kanbai Tunnel it is roughly another minute to the First Kanbai Tunnel and the Teburiyama Aqueduct. Three tunnels and an aqueduct in quick succession make this the point where the ride stops feeling like a valley floor and starts feeling like a gorge.

Visiting

The Watarase Keikoku Railway Third Kanbai Tunnel sits on live single track. Walking in, or entering the track area at all, is not possible, so the tunnel is seen from a train window. Ordinary services between Omama and Kamikanbai pass it, as do the open sided Torokko Watarase Keikoku and Torokko Wasshi trains that run mainly from March to November. Those two need a Torokko seat coupon in addition to the ordinary fare, priced from 1 September 2026 at 700 yen for adults and 350 yen for children, and booking ahead is the safe course.

For hopping on and off, the one day free pass costs 1,880 yen for adults and 940 yen for children. The line runs 44.1 kilometres from Kiryu to Mato and takes about an hour and a half one way. Photography from inside the carriage is unrestricted, but drone filming of the track area and of trains is prohibited outright. Operating dates and times are published on the company website; fares and schedules here were checked on 13 September 2026.