The student union building, slated for possible destruction, isn’t ordinary, says Rowan Moore. It’s “a manmade terrain of rooms and spaces – large, intimate, sociable, secluded, high, low, top-lit, side-lit – which, grouped around a plunging and generous staircase, help you see the banks of green on the other side and feel the slopes of the ground. It is a way of being in the gorge while also – as a human being rather than a bird – using the facilities offered to human students.”