Is it a cruise? A boat tour? A voyage? No, it’s a seatrek, according to our adventure tour operator Explore – to take us to places we wouldn’t otherwise reach (how true, we found out later) around Djibouti’s Gulf of Tadjoura.

To be honest, few of us knew where Djibouti was. The tiny former French colony, which still has a Foreign Legion base, is tucked away in the Horn of Africa, surrounded by fairly daunting neighbours – Somalia, Eritrea and Ethiopia.

But as we bounced out of the harbour in our small, 18-passenger, wooden motor yacht, dwarfed by huge tankers and container ships, Djibouti looked rather like Hull in its heyday. Strategically situated between the Red Sea and Gulf of Aden, the modern port is Djibouti’s raison d’être, the conduit for goods that are hauled by train or by road to landlocked Ethiopia.

As the cranes and docks receded, hazy hills beckoned and we found ourselves chugging back into a biblical timewarp. There were no hotels, shops, paved roads or vehicles, and the only transport was a camel caravan carrying salt silhouetted against the dunes on the horizon. Djibouti’s capital may be a buzzy city, but its countryside is Africa in the raw.

Our motives for choosing the seatrek varied from “more relaxing than a land tour” from Jill Morris, an EU executive, to “a fascination with the sea, but I’ve never fancied a normal cruise – too formal, too dressy, too much razzmatazz”, from Jennifer Newman from Wimbledon. “This kind of trip attracts a lot of single holidaymakers [60 per cent in our case] and as I knew I’d have to share a cabin, I guessed it would be with a like-minded soul,” she said.

As shipmates we were a motley crew of lecturers, teachers, corporate lawyers, engineers and executives, aged between 30 and 60, perhaps our only common denominator a passion for travel, and CVs that notched up destinations from the Antarctic to Zanzibar – which made for instant bonding. We had no television, no electronic toys on board, even our mobile phones didn’t work, but in the evenings, on deck under the stars, we were all transformed into icons like Ranulph Fiennes and Dervla Murphy. We were backpackers who had grown up, with less time to travel, but unable to scratch away the itch.

Informality was the keynote afloat. As we stepped on board we kicked off our shoes and, apart from swimsuits, shorts and sunhats, most of our luggage remained packed. We sun-bathed on mattresses on the deck, and read or gossiped under a shady canopy. At least once a day we dropped anchor to snorkel or swim from deserted beaches surrounded by bare hills. We were rarely out of sight of land during the entire week.

Anyone needing pampering should steer well clear of this type of “no frills” holiday. You are expected to carry your own luggage and make your own bed. The cabins are en suite, but the bunk bed for the second person was little more than a shelf, and the “cons” were anything but “mod”. Air-conditioning was switched on for only three hours a day to save the ship’s batteries – most passengers sharing cabins preferred to take their pillows and blanket on deck to sleep and loved it. Meals cooked by Abdu, one of our five local crew, were simple, often vegetarian, and our big treats the delicious barracuda, snapper or tuna that Basil, the boat boy, caught from the deck.

About half of us took up the excursions, numbers dwindling as the week progressed, and the lazy rhythm of life on board took over. Rachel and Tim, who had ticked off eight previous Explore trips, found the outings expensive for what we got.

But it was the complimentary excursion to Lake Assal that was the most compelling. One of the most ravaged landscapes on the planet and the lowest point in Africa, the lake is an inferno of searing heat, blinding light and sulphurous fumes; for the enthusiast it’s a fabulous geological laboratory of volcanoes, salt lakes and tectonic plates. From this point, Africa’s Great Rift Valley begins to cleave its way south as far as Mozambique. The rift, as our guide explained, widens a fraction every year, and will in trillions of years split Africa in two. Already a new bit of road built over the split has an inch-wide crack across it – rather eerily, in one step I was able to straddle two future continents.

For most passengers however the highlight was the sea itself. The Gulf is an underwater treasure trove for divers and every day our little flotilla of snorkellers combed the reefs identifying sweetlips, wrasses and clownfish. Liz cancelled an excursion because she had fallen in love with a turtle; lecturer Richard, previously a modest swimmer, turned into a waterbaby.

It was an entirely fitting finale on our last full day that one of the great leviathans of the deep made its dramatic appearance. Had we been in the water at the time, we’d probably have swallowed our snorkels in the blinding panic to get back on board. Whale sharks, the largest fish in the sea, can reach up to 15m (50ft) in length, but live off plankton.

Even though we were assured that whale sharks are completely benign (to human beings, anyway), we hesitated before donning our masks and jumping overboard to swim alongside our gentle giant. You can’t do that on a conventional cruise.

Need to know

Jill Crawshaw travelled with Explore (0844 4990901, www.explore.co.uk). The cost is from £1,404pp for the nine-night trip, including flights, transport, six nights afloat and a nights’ B&B in a hotel. The next Djibouti Seatrek departs on March 12, 2008, with additional departures on March 26, April 9, October 22 and in November and December.
Further reading: Africa (Lonely Planet, £21.99).

Indian Ocean odysseys

Elite Vacations (01707 371000, www.elitevacations.com) offers sevennight cruises around the Seychelles aboard a three-masted schooner. All cabins are en suite, prices start at £2,244pp.

The Africa specialist Journeys by Design (01273 623790, www.journeysbydesign.com) will tailor-make three nights at the luxury Manda Bay hotel on Lamu and three nights on a private dhow just for you, with full board, internal flights and transfers, but not flights to Nairobi, from £2,200pp.

Kuoni (01306 747001, www.kuoni.co.uk) has holidays in the Maldives. Seven nights’ B&B at Four Seasons Resort Kuda Huraa with a three-day cruise on a luxury catamaran start at £2,407pp, including flights. Seven nights’ full board at the Banyan Tree Madivaru Maldives hotel and a night on a luxury gulet, including flights, start at £4,575pp.

Times recommends

• New York's top 10 new hotels
• A Scottish monastery retreat
• Welcome back to Rwanda