Along the scenic Agatsuma Gorge in Higashiagatsuma, Gunma Prefecture, there was once a remarkable railway tunnel known as Tarusawa Tunnel. Measuring only about 7.2 meters in length, it was once widely known as the shortest railway tunnel in Japan.
The tunnel was located on the former section of the JR East Agatsuma Line between Iwashima Station and Kawarayu-Onsen Station. Carved through a small protruding section of the mountain, this unusually short tunnel became popular among railway enthusiasts and visitors and was affectionately regarded as one of Higashiagatsuma’s unique “railway heritage” sites.
Following the relocation of the Agatsuma Line in 2014, the tunnel was no longer used for regular railway services. Today, however, the former railway line has found a new life as a tourism attraction, bringing renewed attention to this tiny but memorable tunnel.
Tarusawa Tunnel was completed in 1946, around the time the Naganohara Line, the predecessor of today’s Agatsuma Line, was opened. It is said to have been constructed during a period of intensive railway development spanning the final years of World War II and the immediate postwar period.
Normally, a rocky section only about seven meters long would have been cut away to create an open cutting rather than a tunnel. At this location, however, engineers chose to excavate a tunnel instead. Several theories have been suggested as to why.
One theory is that the rock was extremely hard and that tunneling was more practical than removing the entire rock face. Another suggests that the tunnel was created to preserve the scenery around a single pine tree growing above it. However, no definitive historical record explaining the decision has been found.
Whatever the original reason, the tunnel’s extraordinarily short length attracted attention and eventually made it famous throughout Japan as the “shortest railway tunnel in Japan.”
The Agatsuma Line underwent a major route relocation as part of the construction of Yamba Dam. Approximately 10.4 kilometers of railway between Iwashima Station and Naganohara-Kusatsuguchi Station were moved to a new route, and regular railway operations on the former line ended on September 24, 2014.
Tarusawa Tunnel itself was located downstream of the dam site and therefore escaped submersion. Nevertheless, it was taken out of service when the railway route was relocated.
The new route passes through the mountains to the south via the 4,489-meter-long Yamba Tunnel. As a result, passengers traveling on today’s Agatsuma Line can no longer see Tarusawa Tunnel from the train.
After Tarusawa Tunnel was closed, the title of Japan’s shortest railway tunnel passed to the Kawajiri Tunnel on the JR West Kure Line, which is approximately 8.7 meters long. Tarusawa Tunnel thus became part of railway history as the former shortest railway tunnel in Japan.
The former railway line, including the area around Tarusawa Tunnel, was given a new purpose in July 2020 with the introduction of a unique tourism attraction called the Agatsuma Gorge Rail Bike “Agattan.”
The name “Agattan” combines “Agatsuma” with the Japanese expression “gattan-gotton,” which imitates the rhythmic sound of a train running along railway tracks.
Visitors ride pedal-powered rail carts that combine mountain-bike-style bicycles with specially designed railway carriages. The vehicles travel directly along the former railway tracks, allowing visitors to experience the old railway route from a completely different perspective.
Groups of two or three people work together to pedal the vehicle forward. The attraction is therefore particularly enjoyable for families and groups of friends.
The gentle vibrations from the rail joints, the rhythmic sound of the wheels, and the refreshing breeze flowing through the gorge create an exhilarating experience that can make visitors feel almost like railway drivers traveling through the mountains.
The Agattan gorge course follows a route of approximately 2.4 kilometers through the spectacular natural scenery of Agatsuma Gorge, a nationally designated Place of Scenic Beauty.
Because the former railway line runs higher than the surrounding roads in some sections, riders can enjoy a sense of openness and a gentle thrill while taking in the dramatic landscape.
One of the highlights is passing directly through Tarusawa Tunnel, the tunnel once celebrated as Japan’s shortest railway tunnel. This provides a rare opportunity to experience a historic railway structure rather than simply viewing it as an old monument.
The route also offers views of the impressive Yamba Dam, completed in 2020. Visitors can therefore enjoy both the natural beauty of the gorge and the scale of modern civil engineering during a single ride.
The seasons of spring through early summer, when fresh green foliage brightens the mountains, and autumn, when the gorge is covered in brilliant fall colors, are particularly attractive times to visit. Riding beneath blooming azaleas or through mountains painted red and yellow can make for an especially memorable experience.
Tarusawa Tunnel is located approximately 4 kilometers west of JR Iwashima Station, along the former National Route 145 near the Agatsuma Gorge. Some sections of the old road are currently closed to vehicles, so access on foot is generally necessary.
Visitors arriving by car commonly park at Jūnizawa Parking Area on the opposite side of the gorge and cross Saruhashi Bridge before continuing on foot.
The walk through the area provides an opportunity to enjoy the scenery of Agatsuma Gorge at a leisurely pace, accompanied by the sound of flowing water and the surrounding natural landscape.
At only 7.2 meters long, Tarusawa Tunnel may be tiny, but its historical significance extends far beyond its physical size.
It represents several important chapters in the history of Higashiagatsuma: the development of railways during the postwar reconstruction period, the major changes brought about by the construction of Yamba Dam, and the transformation of an abandoned railway line into a new tourism resource.
Although trains no longer pass through the tunnel, visitors can experience the former railway route in a new form through the Agattan Rail Bike. Riding along the old tracks while surrounded by the mountains allows visitors to connect with both the natural environment and the history of the railway.
When visiting Agatsuma Gorge, consider exploring Tarusawa Tunnel and experiencing Agattan. This tiny tunnel offers a fascinating glimpse into the much larger story of Higashiagatsuma and its changing relationship with railways, nature, and tourism.