It started off as a handful of events taking place in Norwich but 15 years later and Norfolk's Heritage Open Days (HODs) continues to grow in popularity.
This year's event - which enables people to explore some of the county's historic venues, some often hidden, - will be the biggest yet with more than 270 places waiting to be explored.
It has become one of the biggest HODs in the country and the programme is now available following the official launch in Thetford - the first time it has been held outside of Norwich.
The event took place at King's House Gardens where there were reenactors, representatives from some of the places which will open their doors in September, and a special cry composed by Thetford Town Crier Mike Wabe.
Lindsey Roffe, from Norfolk HODs, said: 'Every year we are staggered and so encouraged by just how much support and enthusiasm there is for Heritage Open Days in Norfolk.
'We're very lucky as that's something Norfolk isn't short of; we have lots of fantastic heritage within our communities and lots of people who are happy to open their doors.'
She added: 'Norfolk has one of the biggest events in the country and we are very proud of that and it is growing year on year. It is a special weekend.'
The programme for the free festival, which will take place from Thursday, September 7 until Sunday, September 10, is available from The Forum in Norwich, Tourist Information Centres and libraries.
It is packed with old favourites, including Norwich Castle, St Benet's Abey, and some which are a bit different, including a tour of a former atomic weapons bunker near Thetford.
And new this year is a tour of Prospect House, Norwich, home to the Eastern Daily Press.
Visitors can see where news stories are written, take a look at the archives and see Mustard TV in action.
The programme has been coordinated by The Forum with support from various councils and organisations from across the county.
There are a combination of drop-in and pre-book events, with booking opening at 10am on Monday, August 7.
For further information on the programme and how to book events visit Heritage Open Days or The Forum
Here are some of the exciting events which are taking place this year.
Norwich:
The Cathedral of St John the Baptist will be holding tower tours. It is the highest vantage point overlooking the city, with views as far as Happisburgh and Great Yarmouth.
Happisburgh:
Be guided by experts along the coastline where the 800,000-year-old archaeological site of Happisburgh was unearthed beneath the beach.
Caistor St Edmund: New to this year's programme is the chance to take a tour and hear the story of Caistor St Edmund's rise and fall as a Roman town.
Coltishall: Open top heritage bus tours are being led by guides from the Spirit of Coltishall Association of the former RAF Coltishall site. There will be commentary around the Second World War and the Cold War.
Thetford: See the Medieval armour and weapons used by soldiers who would have defended the town's Castle.
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