Hidden away from the public eye for 364 days of the year it is an untouched haven for wildlife where deer roam free and cranes flutter among the grasses.
But on Sunday the gates to Heigham Holmes nature reserve were thrown open to a curious public, who flocked to the secret island to stroll the marshes and explore its tucked away treasures.
Lying on 500 acres down a narrow country lane in a secluded corner of Martham, the picturesque grazing marshland is home to a plethora of wildlife including redshanks, lapwings and snipe which are in decline elsewhere but thriving here.
The reserve is managed by the National Trust, which holds guided walks around the island at least once a month. But yesterday's open gate session is the one day of the year that visitors can wander through its lush surroundings as they please.
The floating bridge – the only one of its kind in the country – that links the island to the mainland welcomed scores of nature lovers, walkers and families who snapped up the chance to discover the secret surroundings.
National Trust staff and volunteers also laid on a range of nature-themed activities for younger visitors, including pond dipping and bird box building.
Among those taking advantage of the open day was the Hunter family from Essex who were on holiday in Martham.
Mum Wendy, 45, said: 'We have wanted to do it for ages. It's the words 'secret island', they're very exciting.'
Dad Ian, 48, added: 'It's curiosity I think because we have seen it so many times from different angles and sailed past so many times.'
Their sons Euan, 10, and Angus, eight, enjoyed the pond dipping after catching several species in their nets.
Great Yarmouth couple Barry and Valerie Moyse decided to come down for the day as they had never been before.
Mr Moyse, 65, said: 'We have seen it advertised so thought we'd come and have a look. Just the walk down from the bridge was nice. You don't know what's on your doorstep.'
As well as a home for wildlife the site also harbours a secret Second World War history after it was allegedly used as an RAF base for the Special Operations Executive, flying Lysander aircraft carrying agents into occupied Europe.
All evidence was removed at the end of the war however, and the files have been committed to archives not to be released for 100 years, but the occasional artillery shell is said to have landed on the marshes by mistake.
Victoria Egan, National Trust countryside manager for the Norfolk coast, said it was nice to welcome visitors to the reserve.
'Because of the sensitivity of the wildlife it's not something we could allow access free access all year so it's nice when people come and have a really good enjoyable day, and take part in some of the fun stuff,' she added. 'We still do find there's quite a lot of people who haven't heard of it and that's why we run the year round events programme so it's not just for when people are on holiday.'
• What's your favourite hidden Norfolk gem? Write, with full contact details, to Letters Editor, EDP, Prospect House, Rouen Road, Norwich, NR1 1RE or email EDPLetters@archant.co.uk
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