This is the famous Big Hole, which is not the oldest diamond mine but is right down town Kimberley.
They have had the sense to make a visitor center where one can go and see it from close. This visitor center also has a very good museum with everything related to diamonds: from the theory of kimberlites (for the non-geologists) to an exhibit with thousands of real diamonds showing all naturally occurring shapes and colours found. It was a great spot which nicely made up for an otherwise hellish town. Though, to be fair, I should say that I met some really nice people in Kimberley and went out for a drink with some of the locals at the motel where I stayed. One of the old guys, who was the carpenter doing the renovations at the motel, took me round town the nest morning showing me the old De Beers office, the diamond sorting center etc.
People in South Africa (mostly outside big towns) are usually very friendly.Yep! 2722 kilograms of diamonds came out of this kimberlite alone. And it is not the best. De Beers best diamond mine so far is near Mesina (You may remember I went to Mesina on my trip to see the Limpopo). It is the richest and has the best diamonds so far, but it is still active and visiting it is not an option.