Best of the west: Australia's largest state offers superb diving and the nation's finest wines

You look for omens on any sea voyage, and the cheeky young seal that was our escort to the sunken HMAS Swan's final resting place in Western Australia's Geographe Bay seemed to suggest a fine day's diving. Gambolling along the surface, flippers stretched towards the spring sunshine, he revelled in the calm seas and blue sky every bit as much as us. He came right alongside just as we reached the mooring buoys, fixed us with his big brown eyes and carefully preened his whiskers before sliding away into the depths.

After being decommissioned in 1996, the Destroyer Escort HMAS Swan became the first Australian Navy ship to be scuttled in order to form an artificial reef and dive site. The advantage of engineering your own shipwreck is that most "natural" wrecks occur in waters hazardous to ships and divers. In contrast, the Swan, which sits on the seabed 100ft below the surface near Cape Naturaliste, offers comfortable diving conditions almost all year round.

Our dive group of four reached the top of the ship's tower at a depth of 20ft and, at around 60ft, we were alongside the bridge. Heading to the bottom, we swam the length of its 380ft hull. Each hatchway we passed teemed with bullseye fish, their iridescent scales creating a shimmering curtain of red that parted as we poked our flashlights into a cutaway section of the stern. Having gained a sense of the ship's scale, we ascended to the bridge and penetrated the wreck via a forward gun turret.

Adjusting to the restricted space, I developed a knack of settling on to my knees while examining one compartment, before launching myself like an astronaut through a hatchway into the next. Employing this technique, I sailed through the crew's sleeping quarters and straight past a row of stainless-steel toilets.

Exiting the ship after a look at the "ops" room with its banks of switches and dials, we drifted up for a closer inspection of the spindly arms of the ship's tower, before a three-minute decompression stop beneath the dive boat.

When the French explorer Nicolas Baudin sailed his two ships, the Geographe and the Naturaliste, into these calm, clear waters in 1801 as part of his quest to chart the western Australian coastline, he surely never imagined that the bay and adjoining headland – which Baudin named after his two vessels – would become a popular diving spot that today is home not only to the Swan, but also to an entirely different kind of artificial reef.

Busselton Jetty is, at almost a mile and a quarter long, the longest timber structure in the southern hemisphere. This alone draws plenty of local and international visitors, and it also accounts for why I needed to arrive at the jetty 25 minutes before a tour of its underwater observatory was due to start; after collecting a ticket at the jetty entrance, I still had a long way to walk.

The observatory's windows revealed hundreds of colourful corals and sponges clinging to the jetty pylons just below the ocean's surface. Giant barnacles used minute feelers to extract nutrients from the water as it surged and swirled around the creaking timbers. A camouflaged cuttlefish fluttered past, its progress interrupted when a cormorant plunged from the jetty to try its luck among a school of yellowtail.

Two divers drifted into view, a reminder that the observatory is as much a prime marine-life viewing location for the scuba- inclined as it is for those who prefer to stay warm and dry.

A stiff sea breeze rifled the bay as I strolled back to shore, my thoughts already turning to what many visitors regard as the primary reason for a trip to Australia's south-west – the Margaret River wineries. These vineyards produce just three per cent of Australia's wine output yet account for more than 20 per cent of its premium wines.

I'd booked a half-day tour that would take in six wineries plus a stop at Bootleg Brewery, one of the area's reputed exponents of the beer-maker's art. My guide for what promised to be a cheerfully unsober outing was John, a roguish Irishman somewhere near 60 who has lived in the area for nearly three decades. "There's so much space and the coastline looks every day as glorious as the first time you saw it; and then there are the wines, well it's a quality of life you'd never find anywhere else."

Our first stop was at Windance, a family-owned winery that has picked up some prestigious medals and trophies, particularly for its cabernet sauvignon.

I began with snifters of the white blends that the region is celebrated for – sauvignon blanc and semillon – before moving on to chardonnay then cabernet, merlot and cab merlot blends. These are the grapes that fare best in the climate and these wines featured at every place that we visited.

The estate names that flashed by as I drove read like a roll-call of Australia's best-known wine labels: Leeuwin Estate, Evans & Tate, Vasse Felix, Voyager Estate, Cullen, Moss Wood. On John's recommendation, I bypassed the big names, setting my sights instead on a few unheralded gems.

Knee Deep winery had exceptionally hospitable and knowledgeable staff and, in something of a coup, recently lured one of Australia's most respected winemakers out of retirement; Flametree winery's 2007 Cabernet Merlot won Australia's most prestigious prize, the Jimmy Watson Trophy, at the Melbourne Wine Show – unheard of for an industry newcomer; Wills Domain's winery restaurant had an unmatched view of the vineyard and its menu was perfect, right down to the superb coffee.

By the time John and I rolled into Bootleg Brewery, any flavour subtleties between the beers were almost certainly going to be lost on me. Fortunately, our host, Michael Brookes, was quite happy to stand around and talk about the cricket: it turns out that Bootleg's head brewer opens the bowling for the Margaret River XI and didn't mind at all about my diminished tasting faculties while there was cricket chat to be had.

By the end of a convivial hour, we'd gone a long way towards solving the Australian team's selection dilemmas and given earnest consideration to the relative merits of Bootleg's Raging Bull, Wils Pils and Sou'West Wheat.

Just as I was recalling to those around me my experiences in Geographe Bay, a passer-by weighed in with the observation that one must be sure never to drink and dive. Sage advice for anyone fortunate enough to find themselves among the bays, beaches and wineries of Western Australia's glorious south-west.

Getting there

*Busselton is two and a half hours' drive south of Perth.

*Perth is served by Singapore Airlines (0844 800 2380; singaporeair.co.uk); Malaysia Airlines (0870 607 9090; malaysiaairlines.com); and Emirates (0844 800 2777; emirates.com).

Staying there

*Amalfi Resort, Busselton (00 61 8 9754 3311; amalfiresort.com.au). Doubles start at A$195 (£109).

*Dunsborough Beach House (00 61 8 9755 3107; dunsboroughbeachouse.com.au). Doubles from A$66 (£37), dorm beds A$25 (£14).

*Smiths Beach Resort (00 61 8 9750 1200; smithsbeachresort.com.au). Doubles from A$220 (£123).

*Injidup Spa Retreat (00 61 8 9750 1300; injidupsparetreat.com.au). Doubles from A$650 (£362) with a hamper.

Visiting there

*Cape Dive scuba boat trips cost A$195/£109 (00 61 8 97568778; capediveexperience.com).

*Busselton Jetty Observatory tours: A$22.50/ £12.50 (00 61 8 9754 0900; busseltonjetty.com.au).

*A "Taste the South" half-day winery tour costs A$75/ £42 (00 61 4 3821 0373; tastethesouth.com.au).

Eating & drinking there

*Vasse Felix Restaurant, Cowaramup (00 61 8 9756 5050; vassefelix.com.au).

More information

westernaustralia.com

kneedeepwines.com.au, flametreewines.com, willsdomain.com.au, windance.com.au