Not every walk needs a summit. This one is flat, it is eight kilometres there and back, and the whole thing runs beside a canal.

The Huddersfield Narrow climbs out of Marsden through a staircase of locks and then stops climbing, because at Standedge it goes into a hole in the Pennines and stays there for three miles. The tunnel is the longest, deepest and highest canal tunnel in the country, and it was dug by men lying on their backs in the dark with candles.

You can walk to the portal in under an hour. There's a visitor centre, a café doing a decent job of a flapjack, and a boat that takes people in on certain days. I have never been in. I go to stand at the mouth of it, which is free and, I'd argue, better.

What gets me every time is the temperature. On a warm day the tunnel breathes cold air out at you — a steady, slightly damp draught that has been underground for three miles and is in no hurry. You stand in a Yorkshire summer and put your hand into a different season.

The walk back is the same towpath in reverse, which sounds like a failure of imagination and isn't. Canals read differently in each direction. Going up you watch the locks and the mechanism of the thing. Coming down you watch the valley, and the moor above it, and the railway on the far side going into its own tunnel a hundred metres from the canal's.

Two tunnels, one hill, a hundred and fifty years apart. You can see both portals from one spot on the towpath, which is the sort of thing this country does constantly and rarely mentions.

Flat, short, no view to speak of. I'd do it again next week.