Hadrian's Wall: The biggest threat to what is left of the wall is tourists who walk on it. Since the 2003 completion of the footpath that runs the length of it, it has become one of Britain's most popular treksPhotograph: Toby Melville/ReutersHill of Tara, Co Meath, Ireland: The ancient seat of Ireland's high kings is threatened by the proposed M3 highway which runs close by and is due to open in 2010 Photograph: CorbisJurassic Coast, Dorset: England's foremost World Heritage Site and important birding ground was threatened by the oil spill from the stricken container ship The Napoli in 2007Photograph: PJ Sharpe/CorbisRoundstone Bog, Co Galway, Ireland: this 2,500-year-old fragile bog is the jewel of Connemara, but is threatened by climate change - heavy rain and long dry spells - and being trampled by thousands of tourists every yearPhotograph: Michael St Maur Shiel/CorbisSherwood Forest: Logging, agricultural and industrial development, and poor conservation practises have decimated this once vast woodland. English Nature is fighting to keep it vitalPhotograph: Britain on ViewNewborough Forest, Anglesey, Wales: One of the most important conservation sites in the UK for red squirrels. If approved, a current plan to restore the original sand dune habitat by clear cutting could spell disaster for the squirrelsPhotograph: Frank Burek/CorbisStrawberry Hill, London: Sir Horace Walpole’s folly in Twickenham which sparked the Gothic Revival craze in the early 19th-century, cannot raise the £8 million necessary to complete urgent renovationsPhotograph: David Churchill/CorbisCorncrake, North Uist: One of Europe's most endangered species can be found in the Hebrides because of the lack of intensive farming and the 'machair' - a unique type of fertile grasslandPhotograph: Michael Callan/CorbisThe Burren, Co Clare, Ireland: Less livestock grazing the land means that scrub plants have invaded and displaced the native plants that once protected the Burren from the wind and rain. Also, more hikers are trampling over it to marvel at the stone relics of its ancient inhabitantsPhotograph: Michael St. Maur Sheil/CorbisBluebell woods, East Anglia: Global warming means that spring arrives earlier each year, so bluebells don't have enough time to mature and set their seeds. Thurford Wood and Foxley Wood in Norfolk still have good blankets of bluebellsPhotograph: Kevin Schafer/CorbisTower of London: “When the Thames does finally overwhelm its banks, several of Britain’s most revered landmarks are at risk, foremost among which is the Tower of London," says co-author Holly Hughes
Frommer's 500 Places To See Before They Disappear, by Holly Hughes and Larry West, is published by Frommer’s Travel Publications on November 6Photograph: Peter Adams/Corbis