Isegami Tunnel

A granite tunnel under Isegami Pass

Isegami Tunnel (伊世賀美隧道, Isegami Zuidō) is a granite road tunnel beneath Isegami Pass at Iwatate in Akegawa-cho, Toyota City, Aichi Prefecture, completed in Meiji 30 (1897) and entered on Japan's national register as a Registered Tangible Cultural Property on 26 September 2000.

People in the valley call it the Old Isegami Tunnel (旧伊勢神トンネル), because a wider bore of the same name took over the through traffic in 1960. The Meiji tunnel runs 308 metres and measures roughly 3 metres across, which is one vehicle wide and no more. A steel bar above the north portal still sets the height limit at 2.2 metres.

The pass carries the Iida Road, the inland route that tied Shinano Province to Owari and Mikawa. Packhorse trains known as chūma moved salt, rice and lacquer along it, which is why the road is also called the Chūma Highway. The Nagoya National Highway Office of the Ministry of Land, Infrastructure, Transport and Tourism describes Isegami Pass as one of the hardest stretches on that whole route, and the tunnel of 1897 is what finally took the traffic off the ridge.

The change was immediate. Once carts could pass instead of pack animals, the volume of goods moving between the Higashi-Kamo and Kita-Shitara districts rose sharply, and the tunnel stayed the main crossing for more than sixty years.

Why Isegami Tunnel is on the national register

The Agency for Cultural Affairs registered the tunnel under registration number 23-0046 in the twenty-fifth round of listings, citing the criterion that it contributes to the historic landscape of the country. The public notice followed on 11 October 2000. It is counted as a single structure, classed under transport and civil engineering works rather than architecture.

Two things make it unusual. The first is the material. The Agency's database records the structure simply as stone, 308 metres in length, and its commentary identifies the fabric as granite throughout, with the lining carried in stone rather than the brick that Meiji engineers normally reached for. The Nagoya National Highway Office explains why: the tunnel had been designed with a brick lining, but the rock strata and the volume of groundwater met on site raised the risk of collapse, so the specification was changed to stone.

The second is scarcity. Of the Meiji-period stone-lined road tunnels once built across the Tokai region, only two survive. One is Isegami Tunnel. The other is Amagisan Tunnel in Izu, Shizuoka Prefecture, opened eight years later in 1905. The Agency's own assessment places the Aichi tunnel among the representative Meiji road tunnels of the Chūbu region.

What to look at

Stand back about 20 metres from the portal before you walk in. The face is built as a horseshoe arch, and the arch ring is doubled: two concentric rings of voussoirs, each dressed to a different finish, so the outer ring reads rougher and the inner one smoother even in flat light. Flanking the opening are pilasters laid in rusticated blocks, their faces left deliberately coarse against the crisper stones of the arch. This combination of rusticated pilasters and a two-ring horseshoe head is exactly what the Agency for Cultural Affairs singles out in its description of the portal.

Above the arch sits the inscribed stone tablet that gives the tunnel its name. It is set slightly proud of the wall and is easy to miss if you drive straight through.

Inside, the granite continues the full length. Run your eye along the springing line where the wall meets the arch and you can follow the coursing without a break. The air is noticeably colder than outside, and in summer the temperature drop at the portal is sharp enough to feel on your arms. Water seeps through in places, which is the same groundwater that forced the change from brick more than a century ago.

Look at the wear on the lower courses as well. Sixty years of carts, then trucks, passed through a bore this narrow, and photographs held by Toyota City show loaded lorries squeezing under the arch in the 1950s. On the approach, the old road still keeps its Meiji alignment, curving in against the hillside rather than cutting through it.

Three crossings at one pass

Isegami Pass now has more than one tunnel under it, and seeing them together explains why the old one survives.

Motorisation caught up with the Meiji bore in the post-war years. In 1960 a second Isegami tunnel opened on National Route 153, 1,245 metres long and wide enough for two lanes, and the through traffic moved onto it. That is the reason Isegami Tunnel was left intact instead of being widened out of existence: it simply stopped being the main road.

The 1960 tunnel has since run into limits of its own. The Nagoya National Highway Office notes that it was built to the Road Structure Ordinance of 1958 and no longer meets current standards for internal cross-section, so large vehicles struggle to pass each other inside. The approaches include curves with a radius of as little as 30 metres and a maximum gradient of 8.71 per cent. A replacement tunnel has been under construction since the groundbreaking ceremony in May 2022, part of the Isegami Improvement Project.

When that work is finished the pass will hold three generations of engineering within a few hundred metres: a hand-cut granite bore of 1897, a concrete tunnel of 1960, and a modern one built to today's standards. Isegami Tunnel is the only one of the three you can walk through at your own pace.

Visiting Isegami Tunnel

There is no gate, no ticket office and no admission fee. Isegami Tunnel stands on a municipal road in open countryside and can be visited at any hour, though the approach roads are unlit and the interior is dark, so a torch is worth carrying and daylight hours are far more comfortable.

By car, take National Route 153 north-east from central Toyota towards Inabu. The old road branches off the modern highway on either side of the 1960 tunnel and climbs to the pass. Allow roughly an hour from Toyota city centre and about ninety minutes from Nagoya. The tunnel is open to vehicles, but the 2.2 metre height bar rules out most vans and campers, and at three metres wide there is no room for two cars to pass, so oncoming traffic means one of you reverses. There is no dedicated car park; a small pull-in near the portal is all there is.

Without a car, the Toyota Oiden Bus runs its Inabu-Asuke line along Route 153, and the stop named Isegami is the closest point to the pass. Services are infrequent, a handful of runs each day, so check the timetable before committing to the trip.

Photography is unrestricted. The portal faces are the strongest subject, particularly in the hour after sunrise when low light rakes across the rusticated blocks and separates the two arch rings. Autumn colour arrives in this part of Toyota in mid to late November.

One practical warning: the Isegami Improvement Project is active nearby, and traffic controls on Route 153 change from month to month. The Nagoya National Highway Office publishes updates on its project page, and it is sensible to look before setting out.