Chris BishopThousands pass it every day, but few have seen inside it. Now one of King's Lynn's hidden gems is set to open to the public for the first time in centuries.Chris Bishop

Thousands pass it every day, but few have seen inside it. Now one of King's Lynn's hidden gems is set to open to the public for the first time in centuries.

This summer, visitors will be able to marvel at the interior of the 15th- century Red Mount Chapel, which stands in the Walks.

Built in the 1480s as a chapel of rest for pilgrims on their way to Walsingham, the Grade 1 listed building was also used as an arsenal, stable and observatory, before being abandoned to the bats which still nest in its nooks and crannies.

Claire Meredith, West Norfolk council's attractions manager, said: 'We're really excited to be opening the doors to the chapel.

'Lots of people came forward as volunteers and they are really keen to share the secrets of this building with local people and visitors.'

Mrs Meredith said the chapel would be open from 11am-3pm on Saturdays and Wednesdays. The �1 ticket also includes admission to the South Gates.

'It lasts all season so you don't have to see them both on the same day,' she added.

Red Mount Chapel was restored as part of a �4.3m lottery-funded facelift for the Walks. Work included two new roofs of copper and lead, internal repairs and the restoration of a tunnel.

Reopening was delayed after thieves stripped the lead. But it was open for an afternoon as part of last year's Heritage Open Days.

'We had 650 people through the door, they were queuing up outside,' said Mark Fuller, the council's principal project surveyor. 'At the end of the day we had to turn a lot of them away.'

Inside, the octagonal chapel is deceptively large. Narrow, winding staircases ascend to the Upper Chapel with its fan-vaulted ceiling designed by John Wastell - the master mason who designed Peterborough Cathedral and King's College, Cambridge.

'A lot of people say it looks like a pillbox plonked on top, like they had in the war,' said Mr Fuller. 'But it's amazing, there's nothing like it in the country or the rest of Europe. There's nothing to compare it to, which is what makes it so difficult to research.'

Graffiti dating back to the 1530s is carved into the chapel's walls, lit by sunlight streaming through its windows.

'A lot of people know the building from the outside, but not many know it from the inside,' said Mr Fuller.

Access to both the chapel and South Gates costs �1. Tickets can be bought at either venue and both will be open on Wednesdays and Saturdays between 11am and 3pm from Saturday until September 12. Entry for under-16s is free but young visitors must be accompanied by an adult.