I must be honest, I'm not too sure how you'd enter if you wanted to - the holes in that fence look pretty tiny to me. But still, nice of them to warn us that it's a construction area... because I'm not sure that the cranes there in the background were quite enough of a clue on their own. :)
By the way, if you're in Cape Town and you'd like to get a closer look at the stadium, visit the Green Point Stadium Visitors' Centre website to find out about the tours and experiences that are available. Paul and I will definitely be making a turn there ourselves very soon...