How do you describe the view to someone who can’t see? I couldn’t even do justice to a canal towpath | Adrian Chiles

A day with some blind and partially sighted walkers has shown me how much I barely notice - and how hard it is to find the right words

How many shades of green are there? Whatever the answer may be, I soon ran out of words to describe them. I was walking north along the Grand Union canal, trying and failing to adequately describe what I could see, to a friend who couldn't. This was Dave Heeley, ultra-runner, who in 2008 became the first blind person to run seven marathons on seven continents in seven days. Today we were walking rather than running - which, with me guiding him, was just as well.

I had guided a blind adventurer once before when I took part in the television series Pilgrimage. One of my fellow pilgrims was the remarkable Amar Latif. We were high up on the side of a deep, lush valley in eastern Serbia. I was focused on the trickiness of the path itself, but Amar kept asking me to describe the vista. I looked down that valley at the mountains in the distance and simply didn't know how or where to start. I had a bash, as there was plainly plenty of material to work with, but didn't feel I had done justice to the richness of that scene.

Adrian Chiles is a broadcaster, writer and Guardian columnist