One of my favourite walks takes in Knocking Hoe and the Pegsdon Hills along the border of Hertfordshire and Bedfordshire. Today I extended my usual route and kept going till I reached the Barton Hills (above). 

 All three are designated as a National Nature Reserve and Site of Special Scientific Interest. Too steep to be ploughed they survived the industrialisation of agriculture and retain the flora and fauna of undulating chalk grassland.