I guess "fun" is defined very differently for different folks so it is difficult to suggest activities. I always recommend the National Botanic Gardens at Kirstenbosch which also offer great views and are beautiful, expansive and interesting.

But tbh at my stage of life my idea of a blissful visit would be to stay in the winelands and do walks and eat in fabulous restaurants in gorgeous settings. Drive to neighbouring towns over scenic mountain passes and enjoy the glorious setting.

Do day trips into Cape Town if you like (say to visit Robben Island or the museums) rather than the other way around.