For all but one day of the year a scenic corner of Norfolk remains hidden from the public.Heigham Holmes Nature Reserve, near Martham, is on a remote island in the heart of the Broads and its 500 acres of grazing marsh on the River Thurne can only be reached via a swing bridge.

For all but one day of the year a scenic corner of Norfolk remains hidden from the public.

Heigham Holmes Nature Reserve, near Martham, is on a remote island in the heart of the Broads and its 500 acres of grazing marsh on the River Thurne can only be reached via a swing bridge.

The site of special scientific interest is usually closed to the public to protect its fragile habitat and species of birds like marsh harriers, lapwing and redshank and insects such as the swallowtail butterfly and hawker dragonfly.

But on Sunday, nature-lovers will have their annual chance to enjoy some of the county's most spectacular scenery when the gates are unlocked.

The reserve is under the stewardship of the National Trust and is home to cattle between April and October as the area forms part of a working farm.

However, during the winter it provides a haven for thousands of wintering wildfowl, including pink-footed geese from Iceland and white-fronted geese from Siberia.

Shy Broadland cranes can also be seen occasionally, and rare bitterns are thought to be living and feeding in the network of dykes criss-crossing the reserve.

Stephen Prowse, National Trust warden for Heigham Holmes, said he was looking forward to taking visitors on guided walks during the open day, which has been organised in partnership with the Broads Authority.

Visitors will be able to follow a trail and climb an observation tower for an outstanding view of the marshes.

Children can take part in a range of activities with an environmental theme such as willow weaving.

Mr Prowse said a camera had been put up in a barn so visitors could see a nesting barn owl and chicks.

He said: "We want to make sure the plant and animal life is protected for future generations. This will be a special chance to catch a glimpse of this beautiful and undisturbed area."

Mr Prowse said surveys had shown species like water vole, harvest mouse and short- tailed field vole were doing well at the reserve and barn owls and short-eared owls had been seen in the winter.

The National Trust is keen to learn more about the history of the site.

During the second world war it was used by the Special Operations Executive (SOE) as a forward landing strip and agents flew from it in black Lysander aircraft to be dropped or picked up in Holland and Belgium.

But the landing strip and associated paraphernalia were demolished after the war and the runway was ploughed before being returned to grassland.

The open day is from 10.30am to 4.30pm and entrance is £1 for adults and 50p for children. Dogs must be kept on leads.

Visitors must get to the reserve via a swing bridge across the River Thurne at Martham ferry. For details, call the National Trust regional office on 0870 609 5383.