Annunciata Elwes takes a look at Hell Gill, a trek that's not for the faint of heart.
An excursion to Hell Gill, which marks the Yorkshire Dales/Lake District border, is often compared to time spent in the belly of Jonah’s whale, a feeling enhanced by the sudden transition from exposed fellside to murky canyon when following the Hell Gill Beck downstream. Ash trees stretch to meet each other 66ft above, shutting out the light.
Not for the faint of heart (or claustrophobic), the peaty water in this 1,640ft-long limestone gash is knee, if not waist, deep and the damp, mossy walls are 3ft wide in places. One suspects only cavers are happy venturing beyond the 5ft waterfall in the middle.
See more of Secret Britain
Kingley Vale, West Sussex: The ancient, twisted yews that are the oldest living things in Britain
Today's Secret Britain spot is a mysterious and magical spot in West Sussex.
Mynydd Carningli, Pembrokeshire: The ancient volcano in the shape of a reclining woman
The peak of this remote mountain in West Wales is the next spot to make our Secret Britain list.
Thorney Island, West Sussex: The beauty spot accessed via a secret button through a barbed wire fence
The beaches of Thorney Island, next to Chichester Harbour, are our Secret Britain selection today.