For once, here's an octagon story that doesn't involve the UFC and doesn't have a canvas bordered by a mesh fence. But it's a stone monument that's just as bucolic, and until now, has been one of Japan's best-kept tourism secrets. It's a mysterious corridor dubbed the Hakkaku Tunnel, dug into a mountain on the country's Kyushu island.

Locals in the nearby town of Misato have known about the structure for years, but only now have outsiders gotten wind of it. To those visiting the site, it resembles a futuristic hallway that wouldn't be out of place on the set of 2001: A Space Odyssey or Ariana Grande's "Break Free" video.

2 Hakkaku Tunnel

But Hakkaku Tunnel ("Hakkaku" turns out to be Japanese for "octagon") wasn't designed for anything resembling a space fleet when it was built in 1915. The structure was meant to accommodate an 18-mile line of the Yuuen Railway, which ran between Kumamoto and the nearby town of Misato.

Architects chose the design to reduce the risk of rocks falling onto the tracks. But while the shape may have been an impressive safety measure, the railway wasn't able to keep pace with Japan's ever-changing economy and the Yuuen company was shut down in 1964, forever abandoning the tunnel from its original purpose.

1 Gothic Vibe

Today, Hakkuku Tunnel serves as a ghost of Japan's industrial past, an apt metaphor for the rather gothic vibe it exudes to tourists who recently discovered the site. Some marvel at how the light hits the perimeter of the structure as if it's ready to whisk them into another dimension.

Others comment on the fact that the seven octagonal rings that comprise the structure don't connect with each other. Between each ring is nothing but open air on one side and the mountain slope on the other, which creates yet another mysterious shadow effect.

Getting to the tunnel itself seems to parallel the otherworldly experience. There are no signs pointing the way, only a Japanese stop sign on National Route 443 after crossing the Toshenebashi Bridge, which leads patrons down a footpath that winds through the wilderness and narrows the closer people get to the structure. It's yet another attraction adding to the mystical exoticism of the Land of the Rising Sun.