Via GameSetWatch an in-depth article on the Alternate Reality Game Network site explaining how Andy Darley found the cube, and completed the first season of the Perplex City game. Written by Darley himself it's an engaging account of what it's like to actually play one of these games, and the process by which the cube's location was discovered. "It was then that I realised I was practically standing on a spot where the topsoil was the colour of the clay that ought to be hidden underneath it. It wasn't 10m from the post, it was slightly further - practically a continuation of the line I'd just investigated, exactly where you'd end up burying something if you walked 10m, stopped, and leaned forward to start digging. Seeing sub-surface clay with just a very thin covering of the material that was several inches thick elsewhere was deeply suspicious." GSW also links to an exhaustive look at an older ARG-in-a-children's-book, the game Masquerade, which is well worth reading up on.