Simon Calder traces Spanish gold from Antrim's coast to Belfast, then sums up the city’s appeal

Today, the jagged finger of rock that jabs north from the coast of County Antrim constitutes part of Ireland's most spectacular shoreline. Lacada Point stands barely a mile east of Northern Ireland's geological icon, the Giant's Causeway. Beyond that familiar, naturally hexagonal masonry lie dangerous waters that sailors accustomed to Ulster's coast have long known about. Four centuries ago, though, they claimed a Spanish warship and 1,300 lives.

The Girona, a galleass (powered by both sails and oars) was part of the Armada: 131 ships despatched by Philip II as part of an offensive designed to overthrow Queen Elizabeth's Protestantism in England and strengthen Spanish hegemony in the Low Countries. She was wrecked a long way from home, in waters that the crew never thought they would have to negotiate and for which they were quite unprepared.

On a fine October day in 2009, the location looks tame. Tourists scamper across the 40,000 tesselated columns of the Giant's Causeway, gently rinsed by a calm Atlantic: "rare and superlative natural phenomena", which is why the shore joined the Unesco World Heritage List. The National Trust, which looks after the site, encourages visitors to go beyond the strange eruptions and climb the cliff path. Few do – a shame, because this provides both a grand view and a better understanding of the fate of the Girona.

The invasion plan hinged on the Armada providing support for tens of thousands of troops who would board barges at the closest part of the Spanish Netherlands to England: Gravelines (now in French Flanders, and the terminus for Norfolkline ferries from Dover.) .

Almost at once things began to go wrong for the "Great and Most Fortunate Navy", with poor July weather in the Bay of Biscay to the Channel impeding their progress.

Much of the English fleet was moored in Plymouth, and set off in pursuit of the Spanish despite their numerical and military disadvantage; Spain's national coffers, bolstered by earnings from Latin America, had paid for the best fleet on the planet. But a combination of indecisive leadership, disorganisation among the land-based forces and nimble tactics from Sir Francis Drake saw them off.

The surviving ships were ordered to take the long and dangerous route back to the safety of Iberia: heading north across the North Sea, then sailing around the far north of Scotland and the north coast of Ireland before finally running south to Spain.

That, at least, was the theory. In practice, only half the fleet that had set sail to beat the English made it back to Spain. Many of the ships were wrecked on the coast of Ireland, which had recently fallen under the control of the Elizabethan government in London. Any seaman lucky enough to survive a shipwreck in theory faced summary execution.

The captain of the Girona, Don Alonso Martinez de Levia, took the risk of landing at Killybegs in Donegal to carry out some makeshift repairs and pick up sailors from other ships. She then made for Scotland. At midnight on 26 October 1588, as the Girona made her way east along the coast, she struck a reef just offshore Lacada Point. Only a handful of men survived the wreck; they were rescued and led to safety by a local lad, Sorley Boy McConnell.

On any normal stretch of coastline this would be quite sufficient a story to draw visitors. But this part of the County Antrim shore is far from ordinary, thanks to Giant's Causeway – attributed variously to supercooled basalt and the island-hopping antics of the legendary Finn MacCool. Tear yourself away from this collision of geology and geometry and start climbing towards an equally odd sight: a set of what appear to be organ pipes, soaring skyward from the side of a hill.

Climb the Shepherd's Steps (161 of them), and the reward is a view that reveals Donegal retreating into the mist to the North-West, while you might make out the ghostly shores of Scotland to the North-East.

You will certainly observe the tectonic calamities that have created the beautiful Antrim coast: an arm of rock laid bare by the elements, exposing strata that tick off the millennia.

The ship's cargo lay undisturbed for almost four centuries at at what became known as Port na Spaniag. In 1967, a team of divers led by a Belgian marine archaeologist, Robert Sténuit, arrived to excavate the wreck. They surfaced with 12,000 objects, including a trove of treasure that originated in Spain's American colonies.

Naval officers aboard the Girona, and their comrades in the rest of Philip II's fleet, carried a remarkable amount of jewellery made from New World gold. The best of the collection is on display from next Thursday at the refurbished Ulster Museum, itself something of a treasure rescued from an unpromising combination of 1920s neo-classicism and 1970s concrete extension.

Walk in to the white cube of the Ulster Museum's newly created atrium and you feel you have stepped into the latest gallery in Berlin or Barcelona rather than Belfast. Steel and glass are deployed to excellent effect to expose the museum's promise and invite you to explore. The museum has the tricky brief of being all things to all visitors, from stuffed owls to fine art and from ancient Egypt to the Troubles. A £17m makeover has opened up the museum, both internally and to the handsome gardens in which it stands, with the added benefit of fine views across the city and much more natural light.

All that glisters on an Ulster afternoon, in the Armada Gallery of the History Zone at least, is gold that arrived in Northern Ireland in the possession of doomed Spaniards. The crucifixes, chains and charms now on display proved futile in delivering salvation. Most ornate of all is the a gold salamander, studded with rubies, still dazzling after four centuries of submersion in the Atlantic.

"I sent the Armada against men," said Philip II when the remnants of his Great and Most Fortunate Navy limped back to Spain, "not God's winds and waves".

Travel essentials: Ulster treasure

Getting there

Fly to the nearest airport to the Giant's causeway, City of Derry, with Ryanair (0871 246 0000; Aldergrove, slightly further away, is served by easyJet (0905 821 0905; and Jet2 (0871 226 1737; Ferries sail from Stranraer and Cairnryan to Larne. Buses pass Giant's Causeway visitor centre. Belfast's Ulster Museum re-opens on Thursday.

More information; 028 2073 1855