Suddenly the open dale is left behind and smooth limestone cliffs close in on both sides. At its narrowest point, this passage is no more than ten metres broad. It is almost claustrophobic. No water ever flows here these days, not even after the heaviest rainfall. Take a closer look at those rock faces either side of you; surely, they must have been sculpted by a flow of water on a biblical scale.
It is quiet here today – maybe all you can hear are the songs of redstarts and willow warblers in the thorn trees above? Yet all about us is clear evidence of what must have been a thunderous process; to the left of the path there is an overhang of rock, this is where an ancient river has undercut into the rock-face and, looking up, do you think that there was once a complete roof above? If so, at some point it must have collapsed, the debris washed away in the powerful torrent.