Stellenbosch to Kleinmond along the coastal road and back. (If the wind is not blowing). It is one of the top scenic road routes in the country imo. Road surface is nice and smooth, too. Go early to avoid traffic, and keep to the side of the road.
Do Baines Kloof pass oitside of Wellington. You can decide if you want to ride there from Stellenbosch.
Perhaps go out to Cape Town. Start in Hout Bay, ride Chapman's Peak, past Cape Point and back via Simon's Town. This is a major cycling route for Cape Town roadies.
Four passes: Stellenbosch. Grabouw, Franschoek, Stellenbosch loop. Leave early to avoid traffic on the first pass. (Sir Louwry's Pass). Stop for a pie at Peregrine Farm stall outside Grabouw.