In a seat of aristocratic opulence, 100 life-size cast iron figures stand looking out in different directions. Clearly they are human, but get a little closer and their faces appear formless, blurred. In spite of this – or perhaps because of it – their every gaze is penetrating. One of the only things we can know about these enigmatic sculptures is that they are all male, for they are nude. Moulded, in fact, on the artist’s own physique. This is Time Horizon, the latest work from English artist Antony Gormley, opening this week (April 21) to visitors of Houghton Hall, an 18th-century estate ho…