Wellington Arch in Westminster

You're standing at Wellington Arch, the great triumphal arch in the middle of Hyde Park Corner in London. It sits on a green traffic island, and you reach it by the pedestrian crossings. Start with the arch itself. There's a single big opening, framed by Corinthian columns. The architect was Decimus Burton. A ceremonial road between Hyde Park and Constitution Hill still runs underneath, and it can be used for official processions.