A storage facility for archiving furniture, products, and artwork in Miyota-machi, Nagano Prefecture, with a guesthouse attached. Designed by Japanese studio nendo, the tunnel-like architecture took shape through a combination of precast and prestressed construction methods. For precast construction, common parts are moulded in a factory and assembled on site. An example of its applications in infrastructure projects is the box culvert (box-shaped concrete structures) used to store waterways, pathways, power lines, and communication lines buried underground.

The guesthouse is composed of four stacked “tunnels” covered with a roof in the centre. In addition to a long, narrow storage room with a depth of approximately 40 metres, there are two smaller storage rooms, but it is envisioned that more will be added to the site in the future as the collection grows. The kitchen, bathroom, toilet, and other water facilities are concentrated on the first floor, and a compact bedroom and a study are located on the second floor.

The windows were made without metal frames as much as possible, and high-transparency glass measuring up to 10 metres in length was fixed into the grooves in the same manner as shoji screens. The gravel and plantings used in the exterior were also arranged in the interior to draw the outside environment into the interior. To make it easier to walk on, the gravel was partially hardened with resin. The bathtub is carved into the floor, such that the water surface aligns with the floor, creating the appearance that the tunnel shape is continuous. The resulting space is less architectural, but rather a project that combines civil engineering concepts with product design details.