I AM on deck, cradling a warming cup of tea, when it finally happens. I turn in to zip my jacket a little tighter, and pull my hat down further, when, suddenly: "Land ahoy!"

After we have been plunging west for three days from Oban, on the western coast of Scotland, a solid jagged triangle has finally pricked the horizon. Although we have passed through the Outer Hebrides, and called in at Tobermory, on Mull, for a night, we have mostly been sailing across wild, churning seas.

With relief that this is soon to be over, I grip the handrail of the Elizabeth G, and squint across the surging, gun-metal-grey waters of the Atlantic at this pin-sized speck. Eventually, it begins to bulk out and fill the sky, its rocky granite cliffs bearing down over us.

This is St Kilda: once the most isolated community in the British Isles. For more than 2000 years, it supported a settlement on the main island of the archipelago, Hirta (the only one that is inhabitable); its inhabitants were often cut off from the mainland for months at a time, and had to be entirely self-sufficient.

Fortunately, St Kilda is home to the largest population of fulmars in Britain, and the world's largest gannet colony, and these birds formed the basis of the islanders' diet. In 1697, it was estimated that the 180 islanders consumed 22,600 seabirds a week.

"This is the most important seabird colony in Europe," our guide, Chris Gomersall, says; and, as we sail into Village Bay - the only safe anchorage on the island - the occasional gannet gliding overhead suddenly becomes hundreds, the air almost clogging up with them as they wheel around the lofty cliffs, whose granite crags are hiding nesting puffins in their thousands. (With 140,000 pairs, this is the largest colony in Britain.)

It is peaceful, the mass of birds an alluring sight. But our arrival brings turmoil: a starburst spray of wings as the birds scatter, soaring over the water or diving across the almost-velveteen green slopes of the central saddle of Hirta, towards the squat dry-stone remains of what were once the St Kildans' homes, huddled along just one street.

St Kilda is one of only a handful of places worldwide to have been awarded UNESCO World Heritage dual status, for its natural and cultural significance. The heart of it all is this street, where we begin our exploration.

We land on a small concrete dock, built in 1901 with govern-ment funding to help connect the islanders with the outside world. Just 29 years later, it proved to be in vain: the last remaining 36 islanders asked to be evacuated, their self-sufficiency ended by illness, crop failures, and the emigration of too many of their young, able-bodied men, tempted away to the mainland and a "better" life. They were accompanied off the island by the last in a long line of missionaries, and his family.

The Times reported of the evacuation that: "The very last night the villagers have held family worship in their respective homes, reading and praying and singing the Gaelic psalms in the traditional manner which has endured for centuries." When they left, they reportedly left a Bible on the table of each house, lying open at the first page of Exodus.

TODAY, the homes of the last St Kildans sit in varying stages of restoration and dilapidation, some housing National Trust for Scotland volunteers, one (Number 3) housing a small museum. Most, though, sit roofless, and, as we wander through their eerie remains, the gusty wind is whipping through their open windows, and the grass grows wild in their front rooms. The most enduring signs that these were ever homes are the bulky stone hearths, fireless now for decades.

The village is home to a small church, where a missionary, the Revd John MacDonald, first preached in 1822. A zealous man, he has been given the credit for establishing Christianity on an island that, having depended on nature for its livelihood, had Druidic tendencies. After him came the Revd Neil Mackenzie, who reorganised the island's agriculture and introduced formal schooling.

Then, in 1865, the Revd John Mackay arrived. He stayed for 24 years and imposed so many religious services on the islanders that too little time was left over for essential tasks such as growing food. The inhabitants never fully re-covered.

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Behind the village looms Conachair, the island's highest point, and our goal for the day. Its desolate peak seems unattainable at first, shrouded in swirling mist; but, as we make our way up the hill that the St Kildans called The Gap, the clouds start to clear in patches. Awe-inspiring views are unveiled, out over the bay and towards the Elizabeth G, now swaying in the stiff breeze.

Stopping to grab a lungful of air - some of the freshest I have ever breathed - I look back over sweeping grassland to the waters of the bay, now winking back at us in the emerging sunshine. The weather on this wild and windy island can never be predicted.

I peel off a layer, and hike on up. Although the climb gets tougher, I am determined to reach the summit, and grit my teeth, plunging first one foot and then the other into Conachair's grassy haunches, using its clumped grasses like a ladder, until the hillside finally flattens out and I can see its crest. At that moment, I spot my first great skua: it sits in the grass a few metres away and watches me with undisguised contempt.

I have been told that these aggressive birds are called "bonxies", thanks to their habit of "bonking" people on the head to push them from their territory, but it is not until we descend across the island's saddle that bird after plunging bird wheels above us, flying lower and lower on each approach. We huddle together almost desperately, and thrust umbrellas, handle up, into the air to ward put them off.

With every heartbeat, another bonxie approaches, passing so close that we can hear the air move between their wings and our eardrums.

The onslaught stops only when we stagger into the protective shadow of the radar station, at the saddle's other side. Not all the birdlife on St Kilda is as cute as the puffins, it turns out.

THOSE skuas would not have made for easy hunting, but the fulmars did. These gull-like birds spend much of their time sitting on the cliffs (the high-est sea cliffs in Britain), and it was here that the islanders captured them.

The island's men were taught to scale the cliffs as soon as they were old enough. Their ability to do so was inextricably linked to their ability to gain a bride; and our last stop on the island is at the Lover's Stone, a point high above the Atlantic where young men would allegedly stand on one foot to prove their agility on the rocks, and, therefore, their ability to feed a family.

Ultimately, of course, this impressive agility was not enough to sustain a community. But, with the humans gone, the birds are flourishing. As we leave, we see this for ourselves: we sail out towards the sea stacks of Stac an Armin and Stac Lee, where they appear white on our approach. I assume they are covered in bird droppings; but I am wrong. They are, in fact, covered in birds -thousands of them.

This time, the sky really is clogged with gannets, and I cannot do anything but stand on deck and stare. The best birdwatching in Britain may take some getting to - but it is well worth the trip.

Helen Ochyra travelled as a guest  of Hebrides Cruises.

TRAVEL DETAILS

Hebrides Cruises (www.hebridescruises.co.uk) sail out to St Kilda several times a year, departing from Oban. In 2015, there are departures on 23 May, 11 July, and 29 August. The six-night cruise costs from £1450 per person, and includes all meals, plus tea and coffee, and wine with dinner. Guests sleep on the boat in basic private cabins, sharing bathroom facilities.

The National Trust for Scotland also operates a cruise, "Shadows of St Kilda", which takes place on 14-21 May 2015 (www.nts.org.uk/culturalcruising). Otherwise, there is a small campsite on St Kilda (for up to six people, for up to five nights only), bookable through the National Trust for Scotland. It is also possible to apply to join one of the National Trust for Scotland's summer work-parties to St Kilda (www.kilda.org.uk). Scotrail trains (www.scotrail.co.uk) run to Oban from Glasgow Central. Journey time is approximately three hours, and tickets cost from £9.80 each way.