Via a reader:
It's not there yet, but Google is adding a gaggle of World Heritage Sites to the Street View feature, and Sterkfontein will be among them. An interesting detail:
Where access by car is not possible, Google uses its custom-made 'trike' – a three-wheeled bike mounted with a camera – to take the images. It will soon be used to collect imagery of the Sterkfontein Caves in SA.
Now, if they will just take us into the Silberberg Grotto...