But none of us was thinking about danger. The water was churning with seals - hundreds of sleek black heads bobbing up all around the boat to stare curiously at us. Not surprisingly, the waters below were also the happy hunting grounds for the great white shark - another good reason to hold on tight. Most of the films on the great white are made here in Walker Bay, just a couple of hours' drive up the east coast from Cape Town.
Enough exciting wildlife encounters for one day? Hardly. Back on dry land, and before driving the few miles to the seaside town of Hermanus where we were staying, we went to meet Michael Lutzeyer, who with other members of his family owns the Grootbos Nature Reserve and Lodge. Set on the mountain slopes above the bay, the main lodge and cottages have superb views over the sea and along the coast.
"We've just got our first ostrich egg," Michael shouted as we arrived and we admired the recently acquired parents.
A team of environmental experts who live at Grootbos helps guests to get the most from their stay - accompanying them on early morning rides, or walks through the milkwood forest - identifying the many birds, animals and plants. There are more than 1,000 species of plants in the Grootbos reserve, including a huge variety of fynbos ("fine bush"). Michael took us around the fynbos garden they had created. "We've put in 35,000 plants in the past three years - 400 different varieties." And he pointed to the bright colourful proteas that I had noticed in vases all over the lodge.
Whales are also abundant here. Between August and December, Southern Right whales migrate to this coast to mate and calve. This is probably some of the best whale-watching you will ever get anywhere.
We had begun our visit a few days earlier, flying into Plettenberg Bay further up the coast, so we could explore the famous Garden Route before driving down to Cape Town. This is a spectacular area of wide beaches and sand dunes, lagoons and lakes, cliffs, deep unnavigable gorges and estuaries where numerous rivers run into the sea. There are forests and nature reserves. It is a Garden of Eden for nature lovers - made even more stunning by a backdrop of mountain ranges, like the Outeniqua and the Tsitsikamma.
The unexpected heatwave that South Africa had been experiencing despite the approach of their winter had turned to rain. For two days the endless downpour obliterated the views and we drove through damp, mysterious passes and along coast roads, only guessing at the hidden panoramic vistas.
Knysna was a good stop on a wet day, with covered walkways and shops selling art work. This region was settled mainly by the Dutch who lived on a diet of sweet potatoes and cut down the local yellow wood to provide furniture and roofing timber for the Dutch East India Company. It was the need for a halfway supplies-and-refreshment stop for the company's ships on their journeys to and from the Far East that was the reason the Cape was settled in 1652. Today, the inhabitants of Knysna have turned their ancestors' knowledge into a highly profitable market in carved and brightly painted wooden birds.
"Oudtshoorn - guaranteed sunshine," our guidebook said. Mildly sceptical, we headed north from Knysna over the mountains. We should have had more faith. As we drove out of the Outeniqua pass the sun began shining brilliantly.
At the Highgate Ostrich Show Farm we learnt about the life of this strange, flightless desert bird that doesn't have a stomach and has to eat pebbles to grind up its food. If pebbles are in short supply diamonds do just as well - 53 were found inside one ostrich. We saw fields of baby ostriches that reminded me of the raptors in Jurassic Park. Stand too near an ostrich and it can do almost as much damage.
I never really felt unsafe in Cape Town - although it's unwise to walk around at night. The city at the foot of Table Mountain has one of the most fantastic settings in the world and the tourist sights are charming (especially the Pan African Market in Long Street).
One morning I was picked up at 6.30 to do a township tour, which began on the edge of Cape Town on a barren expanse of overgrown weeds and rubble. This was District Six, which at the end of the last century was the sixth municipal district of Cape Town. It was home to a great mix of different people who lived well together, but in 1966 was designated a "whites only area". It took 15 years to move everyone out and bulldoze the place out of existence. Only the churches and mosques were left standing and today in the Moravian Church there is a permanent exhibition to District Six. A map of the streets has been drawn on the floor and people who once had homes here have scribbled their names on the streets where they lived - and brought in mementoes of those days. Even the man who was ordered to dump all the District Six street signs in Table Bay kept them hidden instead, and these are now on display.
From District Six, we drove down to Langa on the Cape Flats - the oldest formal black settlement in Cape Town created by the British in the 1920s for migrant workers from the Homelands. It was called in those pre-apartheid days "influx control". I didn't know what to expect but our guide pointed out the changes: the old pass office at the entrance had become a petrol station and there were some new houses among the many shacks. Even public telephones had been installed.
Progress? At our second township, Khayelitsha, we saw how much change was still needed. "This town is 12 square kilometres and officially houses 450,000 people - unofficially it's probably just over a million," Peter told us. We met Golden, who makes flowers from disused drinks cans to sell in the city shops. Then on to Rosie who runs a soup kitchen from her small house. Rosie is given the cooking equipment and food and keeps what she charges. "I cook for 600 a day," she told me, "and charge the children 10 cents for a bowl of soup."
A few days later, on the way to the airport we passed yet another vast township separated from the road by a ditch and a bank. Along the top of the bank was a line of small shiny, silver cabins. "Are those what I think they are?" I asked my driver. "Yes," he said. "Things are getting better - not long ago we only used to see one thing on that bank. Rows of bottoms." There was no end to the small moments of inspiration provided by the new South Africa.
Valerie Singleton travelled as a guest of Carrier (tel: 01625 582006). The holiday, including return flights from London to South Africa, car hire for six days, and six nights' room-only accommodation, is pounds 1,222 per person.