Japan Travel: Explore a mysterious hidden octagonal tunnel in the mountains of Kyushu

Come with us as we take you off the beaten path to a spot tourists are yet to discover.

While most people who visit Japan journey along the well-beaten path between Osaka, Kyoto and Tokyo, there’s a whole world of breathtaking sites and hidden discoveries lying outside these urban areas. Today we’d like to introduce you to one of these hidden sites, which is well-known to locals but still yet to be discovered by tourists, and it’s located well off the beaten track, tucked away in the mountain town of Misato in Kumamoto Prefecture, on Japan’s southern island of Kyushu.

With no train access, Misato can be accessed in about 30 minutes by car and 90 minutes by bus from Kumamoto City, and with a population of roughly 10,000, it’s a quiet, peaceful locale that’s best known for its historic stone bridges.

Toshinebashi Bridge, for example, is about 24 metres (78 feet) high, and was built in the Taisho period (1912-1926) to carry the main traffic on the prefectural road. It’s an impressive structure, particularly considering the number of stones used in its construction approximately a century ago.

We were interested in checking out another man-made structure while we were in the vicinity: the mysterious octagonally shaped Hakkaku Tunnel. Located off National Route 443 near the Toshinebashi Bridge, the tunnel is hidden from the main road with only a small sign at the carpark in front of the path leading up to it, written in Japanese.

It’s a 200-metre (0.1-mile) walk from this sign to the tunnel, and with nobody around as you walk the leafy mountain path towards it, you quickly begin to feel as if you’re walking through the home of magical creatures from a Studio Ghibli anime movie.

The comforting crunch of the leaves beneath your feet is all you’ll have to keep you company, and as the path narrows near the tunnel, things start to feel a little creepy.

As you walk around the winding path, the tunnel gradually begins to appear, presenting itself with a mysterious aura that causes your jaw to drop as you begin to take in its unique appearance.

Entering through the first octagonal opening feels like entering another dimension. Part sci-fi, part steam-punk, part fantasy game world, it’s not just the structure itself but the eerie stillness and the way the light hits it that makes it feel so otherworldly.

The tunnel is made up of seven octagonal rings, and walking through them makes you feel like you’re travelling in a time machine, creating a mixture of emotions ranging from awe through to fear, excitement, and exhilaration.

▼ Warping through space and time in the octagonal tunnel is a lot of fun.

Delving into the mystery of the structure reveals it was actually constructed back in 1915, when the Yuuen Railway opened in the area, running for a total length of 28.6 kilometres to Misato from what’s now known as Kumamoto City. Hakkaku Tunnel (Hakkaku translates to “octagon”) was designed to prevent rocks falling from both sides onto the railway, but the reason why it consists of seven unconnected octagonal arches is still a mystery.

There are several theories behind it, the most popular being that it was an attempt to reduce construction costs. It was abandoned when the railway closed in 1964, but now, 50 years later, it remains as a site for people to connect with the area’s industrial history.

We’ve yet to meet another tunnel with such a mysterious pull, and we highly recommend seeking it out whenever you’re in the area. The most memorable sightseeing spots are often those you have entirely to yourself, and we’re glad this one is out of the way to save it from being overrun with tourists and Instagrammers.

If adventures like this make you hungry for more off-the-beaten path discoveries, you might want to check out this otherworldly power spot and the edible insect vending machine, both also located in Kumamoto Prefecture.

Site information

Hakkaku Tunnel / 八角トンネル
Address：Kumamoto-ken, Shimomashiki-gun, Misato, Komushiro
熊本県下益城郡美里町小筵

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