The Teff, a perennial stream, rises at Spring Head at the north end of Teffont Magna, and flows some 2.5km south to its debouchment into the River Nadder.

Pyanfar jogged soft-footed as far as the debouchment, where the yellow access tube gave over to descending rampway, a slope of interlocked gratings leading down to the pressure gates, and down again, a long exposed walk to the dock.

The sound of deep singing died away, and as Doyle paced restlessly up and down in front of the Cathedral, he heard that noisy shuffling and murmur of conversation that told of the imminent debouchment of several hundred men and women of precise military bearing.

A simple path descends into the crater at the western end to reveal the place of debouchure of Great Douk Cave, a stream emerging in a small waterfall: a picture for the camera.

The Teff, a perennial stream, rises at Spring Head at the north end of Teffont Magna, and flows some 2.5km south to its debouchment into the River Nadder.

Pyanfar jogged soft-footed as far as the debouchment, where the yellow access tube gave over to descending rampway, a slope of interlocked gratings leading down to the pressure gates, and down again, a long exposed walk to the dock.

The sound of deep singing died away, and as Doyle paced restlessly up and down in front of the Cathedral, he heard that noisy shuffling and murmur of conversation that told of the imminent debouchment of several hundred men and women of precise military bearing.