Discover The Underground Lake of Ohya

Once a negative legacy of the 20th century, after its curious fate, Ohya district turned into a Japan Heritage. 30minutes by bus from JR Utsunomiya Station in a secluded town, Ohya, the area once flourished as a massive quarry with 119 companies at its peak, now has six left. The stones excavated from this region are known as Ohya stones and are a type of tuff. Stretching over 4km from east to west and 6km from north to south above ground and many more miles below ground, these stones are soft, easy to process, and heat resistant. In ancient times, there are records of it being used for stone coffins and for the foundations of castles. It was not until the Edo period that it came into common use, like farmers' storehouses and stone walls surrounding houses. Not just houses and castles, but Matsugamine Catholic Church founded in 1932 is built with Ohya stone too. It is built in the Modern Romanesque style of architecture and is registered as Japan’s tangible cultural property.

Matsugamine Catholic Church

Ohya Stone

Quarrying flourished in the postwar Showa era with its peak production around the 1950s. At that time, 2,450 stonemasons were working here in Ohya. On the other, the shipping volume was at its highest in 1973. As mechanization progressed, the number of stonemasons decreased along with the stone industry. With the spread of concrete and the importation of cheap stones from overseas, Ohya’s stone industry shifted to tourism. The charm of the Ohya had an unexpected twist in its life, one being under the glorious spotlight after the Great Kanto Earthquake in 1923. While most of the wooden buildings had gone in fire from the earthquake, the former Imperial Hotel made by Frank Lloyd Wright, which used Ohya stone, survived. It was this earthquake that made Ohya stone known widely across the country. However, the charm of the Ohya goes under an unexpected fate with the ground cave-in incident in 1989. This had a negative image for the Ohya district and tourism faded away with people leaving and making the area abandoned. Most of the quarry was left untouched, with the leftover underground space created by the quarry still filled with groundwater from rainwater and other sources.

Former Imperial Hotel (now stored at Meiji Mura Museum)

30 years after the incident, Ohya comes back to the media. Strawberries that are not very tolerant of heat were not suitable to be cultivated during summer. But, the groundwater and the air had an annual temperature between 5 to 10 degrees. Piping up such cold energy, the cultivation of strawberries became possible even during summer.
Aside from using such cold energy from groundwater to cultivate strawberries, two of the four local business owners who began this project to revitalize Ohya came up with a unique idea. It all started in 2015 when a team of those outdoor experts came up with an idea that it would be fun to float a boat at the underground lake. After kayaking through the underground lake and rediscovering its charm in 2013, the OHYA UNDERGROUND TOUR was finally opened to the public in 2015.

All of these relics are private property and off-limits, but the tour guides got special permission to enter the mountains from one of the former business owners of the quarry.
This is a project to revitalize the Ohya area by focusing on the former quarry site, which had been considered worthless by the landowners who had closed their businesses, as a material for sightseeing tours, and transforming it into something valuable by creating a story and concept. The tour is both educational and a great thrill to visit the relics to go back in time. There are notebooks, yet to be carved out stones, helmets, trolleys, and many others still left untouched at the former quarry sites. And also, surprisingly, a 40-year-old jar of pickled ume (plum) was left at one of the stone buildings.

Actual notebooks with records of stonemasons entering the tunnel

The tour takes approximately three hours. All you will need is a sweater or light jacket as the underground lake is quite chilly. No comfortable walking shoes are required as the tour includes a free rental of knee-high rubber boots to keep the visitors dirtless and dry. At the beginning half of the tour, visitors will be dropped off at current quarry sites to get familiar with how these stones are excavated and carved. The tour guide will share plenty of tales about the fascinating history of quarrying in Ohya along with many trivia.

Stones are carved and cut with the chainsaw with diamond blades. Before these machines were made, stonemasons had to swing the pickaxe 3000 times to cut out the stones.

The stonemasons go down the long stairs on the left to excavate Ohya stones

Out of the six companies left in the Ohya region, five do underground mining and one does strip mining. There is a reason why underground mining is better for this particular stone. Oya stone was initially extracted by manual excavation using a pickaxe and later mechanized to increase in production which peaked in 1973. This Oya stone is porous and has characteristic brown dots called “miso” formed by the argillation of volcanic ash. Just like the miso used in miso soup, the miso in this stone is clay-like in texture. It is considered that the smaller the miso, the more beautiful the surface becomes, and the higher the value of Oya stone. The stratum of Oya stone is a sandwich of layers of clean stones and layers of poorly formed stones (the part containing miso). Therefore, stonemasons had to dig down deep to get to the part without miso, which made underground mining a popular method. Throughout the tour, there are remnants of how stonemasons excavated along with noticing different quality of stones at the former quarry sites. While there are different qualities, the highest has a tiger like pattern and is called "Toramoku". This is the rarest of all and currently very difficult to find.

Ohya stone with miso

Storehouse made in Meiji Period with the highest quality Ohya stone called Toramoku. This can be seen during the latter part of the tour.

While underground mining seems better, strip mining was the most popular form of mining for Ohya stones in the days before the Edo period, when Oya stone mining was not yet popular. However, as technology progressed, underground mining became the mainstream. Two methods of mining, Kakinebori (horizontal) and Hirababori (vertical) were used to excavate Ohya stones. Kakinebori (horizontal) excavation is a method of cutting stone vertically, and then digging through it in a horizontal direction. After quarrying horizontally, with horizontal excavation, hirabori (vertical) excavation was used to dig downwards into the rock. This method was passed down to Ohya by the stonemasons from Izu between the end of Meiji and the early Taisho period. These quarries stand as relics to the ingenuity of stonemasons who made them and can be observed up close during the latter half of the tour.

Remnants of excavation

The latter half is the most exciting part of the tour. It includes a short hike around the mountains as well as an underground lake boat ride to visit the relics of former quarry sites. For safety reasons, depending on the weather and the physical skills of the participants, this hike may change its routes. Now that the participants have some knowledge about Ohya stone and the quarry, it is time to go on an adventure. Coming across an open space, once a lounge, a toilet and a bathroom, the stone building still stands as it was a few decades ago. These are made by stacking the stones with just the mortars. However, due to the current Building Standards Act, if this resthouse collapses, it has to add a rebar to be rebuilt.

Resthouse on the left, toilet on the right

Trekking through the dense woods and hilly terrain, participants will be able to see where the mining took place. There are tons of things to see and discover, and participants will be busy looking around.

After hiking, participants will go inside one of the mines which were rented out as a military base. Without turning on any lights, the tour guide will take the participants deep into the mine for a surprise. Only the strong-hearted should dare to enter the darkness.

The final part and the highlight of this OHYA UNDERGROUND TOUR is the underground lake boat ride. Once hiking and a bit of exploring around the quarry are done, participants will enter through a locked gate that leads to another quarry. The cave and the lake are lit with subdued colorful lights, making it an unforgettable experience. Reminding somewhat of the boat scene from the Phantom of Opera, participants will get on a rubber boat to start their final quarry exploration. Since the annual temperature here is between five to ten degrees celsius, it is a bit chilly here.

The ceiling is slanted at an angle of ten degrees, and the tour guide will go as deep down as possible. At some point, participants can even touch the ceiling.

While this final adventure seems like a casual boat ride inside a typical quarry, the fun begins when the guide docks the boat at an entrance, just barely enough for one person to go through. It doesn’t seem low from the picture but participants will need to get low to land and keep on moving until the ceiling is high enough to stand.

Stepping into the darkness, the guides will light the area for safety reasons to let the participants know how far they can go inside this cave as the edges are cut off with no fences. This boat ride is unique to this one-of-a-kind tour and can not be missed. Especially the ceiling of fog created from the cold air from underground mixed with the hot air coming in is kodak moment.

Before or after the tour, participants and also, anybody are welcome to drop by at OHYA BASE for drinks and snacks. With an open floor plan, the cafe is a great place to gather information about the areas as well as a place to chill in this cozy place.

OHYA UNDERGROUND TOUR can be directly booked via there webpage here.

Once exiting JR Utsunomiya Station West Exit, go to bus stop 6.
From there, take the bus bound for Oya/Tateiwa and get off at Oya Kannon Mae. It's about a few minutes from the bus stop to OHYA BASE where the tour meet up is.
There are only one or two buses per hour. The total bus ride is about 30 minutes.

OHYA BASE

Tochigi Utsunomiya-shi Oyamachi 1240

0286788657

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