The commission was for a wayside chapel: a roof, a bench, somewhere for a walker to be out of the wind for ten minutes. The client, a parish with a small bequest, asked for something that would last. The architect, Nadja Furrer, gave them a building without a door, and then spent a year explaining why.

The chapel is a gable of in-situ concrete, 9 metres to the ridge, 6 wide, 14 deep, with walls 400 millimetres thick. It would be a bunker if not for the slot: a vertical opening one metre wide that runs from the ground to the ridge on the valley-facing end, open to the weather, and left open.Footnote 1: The slot is set slightly off-centre, so that the two halves of the gable are not quite symmetrical. Furrer says this was to stop it looking like a logo. There is no door because there is no threshold to defend. The wind comes in, the snow comes in, and so do the walkers.

Inside, the slot is answered by a second one in the roof, so that a line of sky crosses the space from end to end. On a bright day the light that falls through is a blade. In fog, it is a soft grey wall. The architect calls it a hinge rather than a window; it is the thing the building opens on.

The bench is a single concrete block along one wall, long enough for eight people or one person lying down. There is no altar. There is a shelf, 40 centimetres deep, at the far end, and people have put things on it: stones, a bicycle bell, a photograph in a plastic sleeve that has survived two winters.Footnote 2: The parish discussed clearing the shelf and decided against it. It is now emptied once a year, on the first Sunday of Advent, and refilled within a week.

Technically the building is close to nothing. There is no insulation, no heating, no electricity, no glass. The concrete was poured in three lifts over a single summer using local aggregate, which is why the walls carry a faint pink that photographs refuse to show. Water that enters by the slot leaves by a channel cut in the floor. Snow that enters stays until spring, in a drift whose shape the walkers have started to anticipate.Footnote 3: A local hiking club now posts the drift’s depth on its noticeboard each week between December and April, next to the avalanche bulletin.

The objection, raised at the planning stage, was that a chapel should offer shelter and this one offers less than a tree. Furrer’s answer was that shelter is not the same as enclosure. You can be sheltered from the wind by a wall that is open at both ends. What you cannot be sheltered from, in a building like this, is the question of why you came in.

It is the most visited structure in the valley. It has no visitor count, because it has no door to count them at.