To see it, “you’ll need to make a 2½-hour train journey from Glasgow to the Highlands, drive 1km into the heart of a mountain and climb a flight of slippery steps on to a viewing platform before you can catch a glimpse: a 48ft x 12ft mural made of wood, plastic and gold leaf, sparkling away at the centre of a vast cave like some fairytale treasure. … Even the artist behind the work has never made the trek to see it in situ.”