Lancashire's Waddow Hall (above) is one of thousands of heritage sites which will be explored during Heritage Open Days in September. Pic © English Heritage
A wind-battered 19th century Dorset tower which inspired a PD James novel, a Hertfordshire mansion used to train sabotage agents during the Second World War and a hydro-electric power station in Devon are among thousands of sites being opened up to the public as part of this year's four-day Heritage Open Days festival.
More than a million people are expected to attend the nationwide celebration of English architecture and history after English Heritage stepped in to rescue the event when previous organisers the Civic Trust went into administration earlier this year.
Clavell Tower, in Dorset, is a literary landmark. Pic © English Heritage
Volunteer enthusiasts across the country will be deployed to showcase the buildings and spaces between September 10-13 as part of European Heritage Days, taking place across 49 countries throughout the month in a mass celebration of Europe's cultural landscape.
Domestic highlights include Clavell Tower on the Kimmeridge Bay World Heritage Site, where efforts to save the 1830 observatory have seen the focal point for James's The Black Tower dismantled and rebuilt 25 metres back from the crumbling cliff it stands upon.
Brickendonbury Hall was used for special agent training during the Second World War. Pic © English Heritage
Literary fans will appreciate the legacy, as Thomas Hardy is known to have courted coastguard's daughter Eliza Bright Nicholls at the scene, as well as using it as an emblem for his Wessex Poems.
Brickendonbury, a grand estate in Hertford, is best known for its role as a training base for resistance workers by the Special Operations Executive during World War Two, preparing combatants for vital operations including a raid to destroy part of Germany's nuclear bomb programme and an attack on the Renault engineering plant in France.
Unexploded hand grenades and live mortar shells were discovered when the on-site moat was drained in 1973.
The Mary Tavy Hydro Electric Power Station. Pic © English Heritage
Devon's largest renewable energy stronghold, The Mary Tavy Hydro Electric Power Station, has bloomed into a highly-effective set of turbines powered by river water, replacing the "primitive" mill wheels it had operated with since 1932, and 9 Dudley Court, one of 25 privately-owned eco buildings across Oxfordshire, will also be revealed.
In Lancashire, the Morecambe Winter Gardens will be revisited 32 years after they closed to the public as local groups step up efforts to restore the Grade II-listed 19th century swimming baths, and the diverse history of Waddow Hall, a 17th century riverside manor which has served as a children's hospital, school and Georgian palace, will be unravelled.
Baroness Andrews, Chair of English Heritage, said the Days were "thrilling". "They are an opportunity to explore places which are normally closed and mysterious," she promised.
"They provide a chance not only to discover secret history, but to meet the people who live or work there and are passionate about their subject. It demonstrates that the great wealth of our culture and history is all around us, on every street to explore for ourselves."
Check out the Heritage Open Days online directory listing for all the events taking place.