Green’s Dictionary of Slang

(S.Afr.) an ironic nickname for Diepkloof Prison, Gauteng Province.

1993		H. Suzman In No Uncertain Terms 145: So in October 1985 I went to the Johannesburg Prison, dubbed Sun City by blacks. This jail, at Diepkloof, just outside Soweto, is an enormous place.
2006		N. Ridley Million-Rand Teaspoon 95: Paul was sent to Diepkloof in the south of Jo’burg. The place was nicknamed ‘Sun City’. Don’t know why.