I’VE BEEN HERE before often, yet on each visit I can never quite believe it’s real. First of all you turn off the main road. Main road? Not exactly a motorway – the long-horned cattle in the field have far more hikers to gaze at than cars. A gate lures you on to a road even less well trodden. To the left a steep bank of oaks rises to the place where we once saw a herd of red deer. To the right, through willows, you glimpse flashes of ultramarine blue on the narrow valley bottom. These are the fish ponds built by the monks at Rievaulx. The ponds are a clue but nothing can fully prepare you for what is waiting when the trees suddenly thin. Reaching a little summit, the path hurries you down through a meadow to where broad stepping stones offer a beck of sheet-glass clarity