Visiting Robben Island is a must of course, when you visit Cape Town. This is where Nelson Mandela was held as a political prisoner for 18 years. The special thing about the tour is that you are guided by former prisoners who can give you a deeper insight into the conditions on the island.
In addition to the historical aspect, taking the boat out to Robben Island is also a great chance to see some seals and maybe even dolphins and penguins!