One of my sons thoughtfully gave me Somerville's Travels as a xmas prezzie. At first glance it looks like a coffee-table book - when you open the pages it is a bit of a treasure. The opening chapter is a journey planner for a 30 mile walk from Land's End to St Ives which takes an inland detour to chun Quoit, Lanyon Quoit and Men-An-Tol. He gives other useful reference books such as Journey to the Stones - guided Walks to the Old Stones of the Land's End Peninsular by Ian McNeil Cooke.
A bit like a walking version the Standing with Stones dvd - Christopher Somerville makes his way north (including northern Ireland) finishing in northern Scotland and Shetland. There is a journey planner with each walk and it would be easy to dip in and out of them if travelling by car.