To the outsider, the culture of the United States appears deceptively accessible. Through its news-media, its literature and its popular music, its cinema and its politics, the country seems forever to be exposing itself, like a cabaret artist, like a monument, like a neon light, to the rest of the world&rsquos gaze. And yet, as Timothy O&rsquoGrady reveals to us as he undertakes a 15,000-mile journey by car, on a circuit around the perimeter of his native land, it is more complex and mysterious than almost any other nation in existence.