To stand on the peaks of mountains is not a given. Helicopter flights are expensive, and the highest peaks are out of their reach. To climb a mountain will require total commitment to the journey, careful preparation, and technical skills. For much of the climb there will be no great views, only struggle and necessary concentration on the task at hand. It is, of course, possible at any time to say "enough", take what enjoyment you can, and start back down; but to do so is to miss the best.

On top of the mountain the trees and clouds are below us, and the sun blazes in an azure sky. For a while after we descend, the resulting tan will mark us out as having been in the mountains, like the fading radiance of Moses' face. Meanwhile we stop for a while, dazzled by light and space, seeing familiar landmarks from an unfamiliar angle, excited by new vistas that open before us like welcoming arms.

Our time on the summit is necessarily limited. It is not possible to live on top of a mountain, except by destroying the qualities that made it desirable in the first place. But the memory of the view will remain long after the horizons have closed in on descent, and we will recognise the other mountains and the far-off places when we come to them, having seen them once before and carried them within us through the valleys and plains.

The far side of the mountain is often a place of cold shadow, and we will think wistfully of the sun and space we left behind. Avalanches and cliffs imperil us, sudden and violent storms blind and overwhelm us. The ground crumbles beneath our feet, and snowfields hide crevasses under a thin smiling crust. The mountains, which shone around us like laughter as we climbed, now shut out the sun, and the valley is bleak and shelterless. We are exhausted, frozen, soaked to the skin, and each hard step brings the choice of whether to live or die - for to stop is to die, and yet to keep moving is to suffer. Even if we live, parts of us may freeze and die here, and we will bear the scars for the rest of our journey.

But every valley contains a river or contains the memory of a river, if you have eyes to see. And the river that shattered the rocks and flayed the mountainside will nourish the plains when its violence is spent. The debris of the broken mountain will form the fertile mud of the plains, cast down in the riverbends that swing through the fields like lazy childbearing hips.

When the tan has faded, when the scars have healed, when the stories have been told in the pub and at dinner parties, what we call normal life will resume. It is characteristic of normal life that it denies the possibility of things being different - this is how life is, it says, how it always was and always will be. Why wish for anything else? Why waste your time on dreams? But the mountains and the valleys will not be denied, and those who have known them carry a secret within them. Like a Tardis, they stand in the corner looking normal. But they are bigger inside than out.