Relax. Enjoy the sounds of South Africa’s Cape Peninsula. The distant murmur of Atlantic breakers. Exotic birdsong. Sprinklers tick-ticking on lush residential lawns. Dogs barking. Suddenly there is something else.

It sounds like the sky inhaling — a sustained, ever-strengthening intake of firmamental breath. All other noises cease. You sit up. The inhalation rapidly segues into an ominous metallic whistle. A black shape streaks overhead and instantly you are engulfed in earth-shaking, ear-wrenching thunder.

Inside that black shape, the thunder is constant and the view changes continually. One moment the sky, seen through the cockpit canopy, is where it should be — up above. Then the plane rolls and the world turns upside down; look up and there is a rush of greenery, then a thin ribbon of golden sand, and then the ocean.

When Concorde retired, many proclaimed the end of the supersonic age. Yet here we are, traveling at close to Mach 2 at high altitude. We’re not here for comfort (the two-man cockpit is cramped, and the harnesses are so tight, they will probably leave bruises), or to fly between destinations (in a moment we will return to Cape Town International Airport).

We’re here for one of the ultimate thrills in aviation: to fly in a jet fighter.

The plane is one of four 1950s English Electric Lightnings operated by Thunder City, a company that boasts the largest privately owned collection of working combat jets in the world. Their fighter fleet is larger than that of the Royal New Zealand Air Force. The company’s other jets include BAe Buccaneers and Hawker Hunters.

The Buccaneer is a low-level strike bomber, and its flight sorties are usually conducted among the valleys of the Cape Swartland Mountains. The Hunter is a highly maneuverable jet, and its program includes plenty of aerobatics. But for brutal speed, the Lightning is the ultimate. At full power, the plane burns more than 130 gallons of fuel every 60 seconds. “That’s the equivalent of 34 car tanks of gas per minute,” said Mike Beachy Head, Thunder City’s CEO and chief pilot.

It’s not surprising then that the flights are relatively short, usually about 40 minutes. But it is an experience that will remain vivid for life. Nobody who flies in a Lightning will ever forget it. Back outside the Thunder City hangar at Cape Town International Airport, we descend the ladder from the cockpit and, with a combination of relief and regret, plant our feet back on solid ground.

It will not be for long. Another element beckons. The following morning we have driven east from Cape Town, along the Indian Ocean coast, to Gansbaai. Here we board a 30-foot cruiser, unhitch from the jetty, and voyage across the rippled sea to a channel between two islands, Dyer (named after an African-American, Samson Dyer, who lived here in the 19th century) and Geyser.

Once we’re in position, the boat’s crew starts “chumming” — a less pleasant activity than you might imagine since chum is a mixture of blood and fish guts. A slick of this noxious substance soon trails in our wake. Wearing wet suits, we sit tight in the gently rocking boat, not talking, waiting for the word that will signal us into the water. If we seem preoccupied, it is not surprising. The word we are waiting for is: “Shark!”

Not just any shark. Those of us who grew up in the 1970s have been conditioned to dread one shark species above all others. Films such as “Jaws” and the terrifying documentary “Blue Water, White Death” established the fearsome legend of the great white shark.

Its perceived villainy has done it no favors conservation-wise, and therefore, in the past couple of decades, marine biologists have sought to challenge Hollywood’s planted perception. The great white is not a psychopathic man-eater, they tell us. In fact, it’s almost cuddly.

“Shark!”

Here we go. One by one, the four of us clamber from the boat into the cage moored alongside. When we’re all in position, making sure our masks are secure, we hook our mouths up to the oxygen supply and the cage descends until we’re completely immersed in the blue-green world beneath the waves.

The top of the cage will never be more than three feet below the surface. Shafts of sunlight penetrate the water, illuminating clouds of plankton and scraps of chum. We try to keep that music (Dum, dum. Dum-dum, dum-dum, dum-dum.) out of our heads, but it’s no good. This is the calm before the frenzy, and the theme from Jaws — cliché though it is — is the only tune you can think of at a time like this.

Now, in the dark blue distance, an innocuous cloud of plankton appears to coalesce. Suddenly there is the creature in question, gliding toward us with effortless grace, a thing of sleek perfection — gunmetal gray above and pure white underneath. As it closes in on the cage, we realize with awe and alarm that it is approximately the size of an average family car — a family car with teeth.

It circles the cage once, then, with a propulsive flick of its massive tail, it torpedoes straight at us. We brace ourselves, gripping the ring in the center of the cage, ensuring that all our extremities are well away from the outer bars. The impact is only glancing. The clank of shark on metal reverberates through the water.

That was merely a playful nudge. When it comes round again, the shark means business. This time it strikes with its jaws open. Its teeth grate against the bars. The cage rocks violently. There is no time to think, or even to be scared. We just hang on and endure the battering. An attack on the cage is highly unusual — but even at the height of it, we can’t help feeling thrilled. This will be an experience to dine out on for years.

Later, sitting safely back on the boat, we begin to understand the true meaning of the encounter. Out here, within sight of the tourist comforts of South Africa’s coast, we have been forced to confront our relative place in the natural pecking order. And we have discovered that one-on-one we are infinitely inferior to the great white shark.

With that humbling lesson learned, we move back onto dry land, setting off for a bush walk a thousand miles to the northeast, in private reserve adjoining the vast Kruger National Park. The wildlife hazards here are as menacing as those we faced off Gansbaai, only this time there is no cage to protect us.

We walk through thorny scrub. Even the trees here can bite. If you brush against the wrong sort of branch, 2-inch-long thorns will pierce your clothing and draw blood. But at least the trees are inanimate and can be skirted easily. When our tracker stops and crouches down, signaling for us to do likewise, we know that we have found something more lethal than a thorn tree.

The tracker puts a finger to his lips, and then dangles his arm in front of his face in crude mimicry of the species he has spotted up ahead. We can hear the sound of branches cracking, and of leaves being ripped and eaten. We are within less than 50 feet of an elephant herd.

The great white shark, teeth and all, is dwarfed by comparison, and is perhaps a less frightening prospect. To confront either animal in the wrong circumstances would be terminal. But with the shark, the end would be swift. Death by elephant would entail a lengthy trampling.

In these tense moments, it is not the theme from “Jaws” that torments us, but rather the premonition of an elephant trumpeting — the sound that would herald a full-blown charge. Our tracker ushers us forward. Step by step, we follow. Every twig that snaps underfoot sounds like a rifle shot. Finally we reach the top of a slight ridge and gain a clear view of the herd. We count 18 of them, nonchalantly tearing a swathe of destruction through the bush in the name of lunch. We are safely downwind of them, and they are safely preoccupied with eating. Our heartbeats begin to settle.

“Look at the baby!” someone whispers.

We are at ease, smiling, enjoying these privileged minutes with the world’s biggest land mammal. Yet this is no zoo. We are in the wild, exposed to the realities of nature. The tracker is constantly alert, listening, watching — keen to the slightest shift in wind direction.

Eventually we move on, treading carefully and silently until the elephants are far enough away for us to be able to walk and talk normally again. Released from the tension, we chatter exuberantly. Half an hour later, back at camp, we continue to relive the encounter over a beer or two. This is the same buoyant feeling that we experienced after cage diving with the shark, and after catapulting over Cape Town at supersonic speed in the Lightning. In each case, we had submitted ourselves to the mercy of forces beyond our influence, and survived.

Are we swearing “never again”? Are we berating ourselves for risking life and limb? Not a bit. In the bar at Thunder City, on the shore at Gansbaai, and in this rustic lodge in the wilderness, when the adrenaline rush has subsided, the conversation switches to the favorite topic of the habitual thrill-seeker: What next?

Unforgettable Adventure

Thunder City (www.thundercity.co.za, tel 27 21 934 8007, fax 27 21 934 8003) is based at Cape Town International Airport, a short drive from the main passenger terminals. The Thunder City experience usually lasts three hours, and includes a full briefing, survival training, ejection-seat training and oxygen management. You will be provided with a flight suit, boots and helmet. Flying time will be about 40 minutes. Prices start at approximately $4,450 for a sortie in the Hawker Hunter. A flight in the BAe Buccaneer costs around $9,550, while the unforgettable English Electric Lightning experience will set you back $12,000. Flights are weather permitting. The company advises that you book your flight for the first day of your stay in Cape Town to enable rescheduling in case of bad weather (an all too common occurrence during the winter months, May through August).

White Shark Ecoventures (www.white-shark-diving.com, tel 27 21 532 0470) offers shark-viewing voyages, as well as cage-diving trips, near Gansbaai. The best time of year is April to September when food is scarce and the sharks are lured to the boat more easily. A full-day dive tour, including transfers from Cape Town, all necessary equipment and instruction, costs approximately $200 per person. If transfers from Cape Town are not required (there are plenty of bed and breakfast accommodations around Gansbaai) deduct $35 per person.

Ngala Tented Safari Camp (www.ccafrica.com/accommodation-1- id-2-7, tel 27 11 809 4300) is the first private game reserve to have been formally incorporated within the borders of Kruger National Park. Threehour walking safaris can be arranged from the camp. For the more adventurous, four-day, three-night walking safaris are also available. Accommodation at the tented camp is from $700 per night, excluding transfers. The three-night walking safari costs $600 per person.