Portsmouth is a place which is full of surprises, starting with the fact that this is the UK's only island city, linked to the mainland by a single road.

I wanted to know why the workaday port I remembered from ferry trips to France should be the centrepiece for this year's SeaBritain Festival and the Trafalgar 200 celebrations. Truth to tell, I'd never looked beyond the M275 road into Portsmouth and the International Ferry Port before.

If I had, I would have known that Portsmouth has been the home of the Royal Navy for more than 800 years and that the city has been busy re-inventing itself as the UK's most striking waterfront city in recent years, all of which helps to explain the SeaBritain connection.

Family in tow, I started my visit at Portsmouth Historic Dockyard, just voted best 'Large Visitor Attraction' in the annual Enjoy England Excellence Awards. Another surprise: I was sure that we could crack it in a day but the place is worth a short break in its own right.

The Historic Dockyard is home to the Mary Rose, the pride of Henry VIII's fleet of warships, raised from the seabed in 1982, as well as to the world's first iron-hulled ship, HMS Warrior 1860, both fascinating in their own right. But in this, Nelson's bi-centenary year, it seemed only fitting that we should concentrate on HMS Victory.

Nelson's flagship fought and won the Battle of Trafalgar in 1805 and it is a splendid black and gold sight in its Portsmouth harbour home. Most impressive, there are three levels of gun decks, crammed full of guns, but the abiding impression is of very low ceilings - no fun for Captain Hardy, a 6ft 4in giant of a man.

Most poignant is the spot on deck where Nelson fell, ironically after victory had been achieved, and, below that, the simple bay where he died.

We dipped into the Victory Museum with its fantastic display of ship figureheads and the funeral barge that carried Nelson to St Paul's Cathedral, and into the Naval Museum, with its clever, educational exhibits for kids.

We stayed longer in the new Trafalgar Sail exhibition, in which HMS Victory's Foretopsail, the only surviving sail from the Battle of Trafalgar, is imaginatively displayed. Flashing lights reveal its surface, pockmarked with 90 shot holes, accompanied by the deafening sound of cannon fire.

The Historic Dockyard is in Old Portsmouth, an area of quiet, cobbled streets full of old inns and traditionally painted houses.

So it comes as a surprise that a stone's throw from the dockyard is the new waterfront entertainment centre of Gunwharf Quays.

It's to this smart harbourside development that the Global Challenge yacht race will return in July and it's also where the futuristic Spinnaker Tower, the UK's tallest publicly accessible building outside London, will open its three sky-high viewing platforms to visitors later this summer.

Meanwhile the opportunity to scour the designer outlet shops and indulge in people-watching from one of waterside bars proved irresistible and a fitting end to our first day. Next day we headed to Southsea and the D-Day Museum.

As with the Historic Dockyard, what staggers is the sheer scale of information provided. It is also the home of the Overlord Tapestry, which, like its Bayeux forerunner, weaves the war's story in impressive detail.

Next door is the Blue Reef Aquarium, where friendly types like the Common Clownfish, a Finding Nemo favourite, are outnumbered by the Golden Poison Frog, whose toxins can kill eight people, and the Gollum-like aquatic Xenopus Frog.

But any visit to Portsmouth must return to the sea and we finished our trip at Southsea Castle, the place where Henry VII stood and witnessed the sinking of the Mary Rose. This would be just the place, we mused, to watch ships from around the globe as they converge on the Solent during this year's International Fleet Review.