The folks at MAD Architects sure are a busy bunch, with a conference center in China, George Lucas' museum and a small hilltop village in LA among its projects to grab our attention this year. Its latest efforts in Japan are certainly no less eye-catching, transforming an abandoned tunnel into a stunning underground art gallery for the 2018 Echigo-Tsumari Triennale art festival.

The Kiyotsu Gorge Tunnel serves as an avenue for spectacular vantage points of Japan's magnificent Kiyotsu Gorge, winding 750 meters (2,500 ft) through its famous rock formations with designated lookouts dotting the route. The renovation carried out by MAD Architect's offers even more eye-candy along the way, with five natural elements used as decorative themes throughout.

First up is "Wood," with a cedar-roofed cafe and souvenir shop offering local crafts and a hot spring foot spa upstairs. The wooden interior of the bath slopes upwards like a volcano to an opening at the top, which is fitted with mirrored lenses to reflect the surrounding scenery.

The passageways of the tunnel have also been illuminated with lights of different colors, each representing the different lookout points and all together intended as a representation of "Earth."

"Metal" is honored at the first of the revamped lookout points, with a reflective capsule housing a toilet and a one-way window covered in metallic film at the tunnel's end. This offers views outward over the gorge only, and is meant to explore the relationship between private and public.

Convex mirrors backed by fiery light adorn the tunnel's surfaces at the second lookout point, with these orange "dew drops" a tribute to the element of "Fire." And the "Light Cave" is the big finale, with the element of water honored by way of semi-polished stainless steel covering of the tunnel's surface. This combines with a shallow pool of water covering the floor to create shimmering reflections of the gorge beyond the edge.

The 2018 Echigo-Tsumari Triennale runs until September 17 in Japan's Niigata prefecture, while the video below provides more of a look inside the tunnel.

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