I can recommend Breakwater Lodge at the Waterfront. The Waterfront is a safe area in Cape Town, even after dark. There are lots of nice restaurants in the area, and food in South Africa represents extremely high value for money. Lodging too, but that is outside Cape Town.
I can also recommend a tour to the Cape of Good Hopes.
If you feel that you have time for it, Durban is an interesting city as well, but in the "other end" of South Africa, so to speak. Pretoria, Port Elizabeth or East London is not worth the visit and Johannesburg is dangerous.
The prettiest landscape is in the far northeast, on the way to Mozambique.