Brighton's Royal Pavilion Gardens has been added to Historic England's most 'at risk' register.
It is now said to be threatened and in urgent need of repairs.
22 sites in total have been added to the register this year.
These include the No 2 Battery in Gosport, Hampshire and Northumberland protected wreck site in Kent.
However 32 sites have been removed from the register.
These include the Argos Hill Windmill in East Sussex, Newbury Battlefield in Berkshire and St John the Baptist Church on the Isle of Wight.
Over the past year, Historic England has offered £612,000 in grants to help some of the region's best loved and most important historic sites.
The Heritage at Risk Register 2017 reveals that in the South East, 89 Grade I and II buildings, 214 scheduled monuments, 94 places of worship, 25 registered parks and gardens and 64 conservation areas are at risk of neglect, decay or inappropriate change.
Brighton's Royal Pavilion is one of our region's most famous landmarks, attracting thousands of visitors each year. But now, for the first time, there's a chance to explore a secret tunnel running beneath it.
The tunnel was built so that George IV, who'd grown very fat and unpopular, could visit his riding stables without his subjects seeing him.
Malcolm Shaw spoke to David Beevers, the Keeper of the Pavilion, and tour guides Meg Hogg and Geoff Greenwood.
A project to revitalise the Royal Pavilion Estate in Brighton has been given a funding boost of £5 million.
The Heritage Lottery Fund has earmarked the sum for the project, subject to plans being successfully developed to the next stage for which they are providing development funding of £176,000 upfront.
Visitors to The Royal Pavilion in Brighton will be able to take part in an audio tour about its history as a military hospital.
During the First World War, the palace's elaborate rooms were transformed in to makeshift wards to treat injured Indian soldiers.
The tour will open next month - marking a centenary since it helped servicemen in December 1914.
It's the jewel in Brighton's crown - and today a £34 million make-over plan was revealed for the Royal Pavilion estate. Over a million people visit the iconic palace, Brighton Dome and museums every year - but there are vital repairs needed - to make it sustainable for the future.
Charlotte Wilkins has been given a tour and has spoken to Brighton and Hove City Council Leader Cllr Jason Kitcat and Chief Executive of Brighton Dome and Festival , Andrew Comben.