Crummock Water and Buttermere, in prehistory both were once part of a single lake until the alluvial fan from the sediments coming down Sail Beck separated the two. Nicholas Size coined the name the ‘Secret Valley’ for Buttermere in his 1920’s book. It tells the story of Saxon and Norman attempts to conquer the Norse settlers of Lakeland. Before the modern road around Rannerdale Knotts was made Buttermere was hidden from view up Crummock Water. In the 1070’s Boethar the Younger chose this hidden valley as his base to defend Lakeland and to carry out guerrilla attacks against the Normans. The name Buttermere derives from Boethar’s mere.