The UK's best cave diving locations – by Martyn Farr

January 23, 2024 6 min read

Otter Hole – Hall of Thirty – spot the two cavers!

Otter Hole – Hall of Thirty – spot the two cavers! 

Few people know of, or appreciate, the sheer magnitude of spectacular sights found underground. We have so many natural caves formed in limestone rock; long abandoned mines where all sorts of minerals and metal ores were extracted; an amazing variety of tunnels constructed for railway transport, or for distributing water, or even those built for military or strategic purposes. There is immense variety in Britain when it comes to these sorts of places.

This subterranean wonderland presents interesting, indeed fantastic, recreational opportunities for people of all age groups and abilities. And it is this fascinating sporting, distinctly challenging, esoteric environment that has inspired people like me for a lifetime.

The sheer depth and length of our caves is certainly noteworthy. British caves may not feature among the deepest caves in the world but given the nature of the chilly subterranean environment these sites are always something of an adventure. Depth refers to the vertical extent of a cave, specifically the difference in elevation between the highest and lowest points within the cave system. The deepest caves are generally characterised by vertical shafts, or steeply inclined passages. In the Yorkshire Dales the former situation is evident, and there are many superb landmarks such as the yawning abyss Alum Pot (104 Metres deep) or the better known chasm Gaping Gill (110 metres deep). These are truly spectacular awesome places for the seasoned British caver and indeed splendid viewing places for outdoor enthusiasts generally. Interestingly it is in the less rugged mountains of South Wales that the overall deepest system in the British Isles, is located. Here in the upper Swansea Valley the cave Ogof Ffynnon Ddu (Cave of The Black Spring) claims a vertical extent of 274 metres. And amazingly, due to the gently dipping rock strata in the locality and the extent of the limestone, it is almost possible to traverse the system from one end to the other without the use of vertical equipment. This together with the bounteous 60km extent of the network makes the cave perhaps the most popular site with cavers in the British Isles.

Gaping Gill – Fell Beck tumbles into the shaft

Gaping Gill – Fell Beck tumbles into the cave entrance  

When it comes to the oft asked question as to which is the most spectacular place in the UK this is more difficult to answer. Each of the sites selected to appear in my recent book Hidden Realms has a special charm. However, trying to be critical I think a particularly fine grotto, or indeed a cave with several of these and perhaps some other attractive feature is the bottom line. So Notts 2 in the Yorkshire Dales, Otter Hole in the Forest of Dean, and Ogof Ffynnon Ddu in South Wales would certainly be prime contenders. In Ireland Crag Cave in Co. Kerry is similar.

Porth yr Ogof – Hywel's Grotto

Porth yr Ogof – Hywel's Grotto

In any discussion on caving people almost always enquire as to the best site for beginners to visit. There are any number of places vying for this position. In my home area, South Wales, there is little doubt that the finest place is Porth yr Ogof in the Brecon Beacons National Park. Well over 30,000 people a year come here to experience a cave for the first time. You can venture just inside as a casual member of the public and with just a simple hand torch you will appreciate the wonderment – large echoing tunnels radiating away mysteriously into the darkness, swirling deep water and tantalising, fascinating arrays of rock formations hinting at the probability of more intriguing sights deeper inside. Yes, there are serious safety considerations for the uninitiated visitor and this is where a guided visit is the recommended next step if the curiosity and allure are sufficiently motivated. Porth yr Ogof will provide a great introduction to caving where, joining a group, you can wander through well trodden tunnels, walk, scramble, crawl, and perhaps squeeze through places you could never have imagined possible before that point. It's simply great fun and you are never more than a few minutes travel from the outside world.


Swildon's Hole – Sump 1 surfacing

Swildon’s Hole – The Twenty Foot Pot from the bottom   

In terms of accessibility, sporting challenge, and evident future exploratory potential Swildon's Hole, near the village of Priddy, in Somerset cannot be overlooked.  This cave is certainly one of the most accessible sites in the UK. It's an easy walk to the entrance and as you follow the stream disappearing into the ground you know you are following in the footsteps of countless thousands of people before you. Swildon's is good clean adventure. It may be wet with quite a few vertical scrambles, or even a ladder pitch, but it’s a joy to experience, at every level of capability.

Ogof Draenen – near Circus Maximus

Ogof Draenen – Formations near Circus Maximus

The history enshrined in the sport of caving is quite amazing. Exploration is a protracted process and is being actively pursued in many caves across the British Isles today. The tales of surprising discoveries, sheer dedication and determination, of incredible derring do render the activity the most exciting of all outdoor activities. Even today we can only postulate the eventual extent of many caves, hypotheses based on various criteria and heavily dependent upon geology and water catchment area. As such the Three Counties System in the Yorkshire Dales National Park must be flagged. Over the last fifty years It has spread like an ever growing spider’s web to capture and link an amazing number of once separate caves extending from Cumbria in the north through part of Lancashire into Yorkshire. This incredible cave network is now over 86km in total length but every year new discoveries are made and quietly, year on year, the system grows ever longer. Many of the sections were originally separated by sumps but today any number of dry by-pass connection routes have been found; ways in which non amphibious activists can travel amazing distances from one cave to another. No matter how exploration occurs it is clear that if the Three Counties System is extended to encompass the caves of the Kingsdale valley we are talking about a labyrinthine network in excess of 100km. And the separation between the two systems is ever so close… In South Wales there is potential for a 150 km long system spread beneath Llangattock Mountain. The longest system in Britain accessible to all with no requirement to dive lies nearby at Ogof Draenen and, while currently an estimated 80 km in length, it again will easily surpass 100km in the future. There is simply so much undiscovered passage waiting to be found right across the limestone areas of Britain.  

Wookey Hole – Chamber 19

Wookey Hole – Chamber 19

When it comes to the most famous cave in Hidden Realms I think the field narrows considerably. In the north of the country Gaping Gill stands proud; in the Peak District its Peak Cavern, while down south few people will not have heard of Wookey Hole at the foot of the Mendip Hills. All have a fantastic history, spectacular sporting terrain and each is a place that every caver aspires to visiting. Wookey Hole has it all. There are the wondrous blue lakes in the show cave with legendary archaeological interest. Here too there are tales of an evil witch, to enthral young and old alike, while at the other end of the adventure scale, there is a fully fledged serious enterprise to reach the furthermost end of the ‘dry’ cave in Chamber 24. And, of course, if you train as a cave diver then you could experience underwater Wookey, the finest and perhaps the most famous site of its kind in the world. Cave diving has always played a major part in the exploration of the British underworld and Wookey is very much the birthplace of the activity.  This site has seen the application of every technological innovation known to explorers, and presents an incredible history documented in the internationally acclaimed book The Darkness Beckons

Dan yr Ogof - Cloud Chamber

Dan yr Ogof – Cloud Chamber

Most caves and mines will present surprises or unusual features. And these are places that have to be seen to be believed. For me experiencing the sudden pulse – a veritable mini tsunami - of water in Speedwell Cavern, in the Peak District,  was quite incredible. There are only a limited number of these places known worldwide so getting to experience a very impressive discharge of water pouring down the passage towards you is invigorating to say the least. On a different note, it may surprise many people to learn that my favourite cave is Dan yr Ogof in South Wales. Yes, it’s a famous show cave and yes it has some of the best formations to be seen in any cave system, but what perhaps is the most difficult to comprehend is the near-death experience that I underwent here in the summer of 1971. I had visited from childhood and from my teens found the lure of first-hand exploration irresistible… so this is where I learned to cave dive.  It was nothing short of a miracle that I survived my earliest undertakings in this sphere and perhaps I should blog this at some point … But since then I have returned hundreds of times and been lucky enough to find a lot of new passage never before, or since, seen by human eyes… This is the ultimate thrill of our sport.


All photography by Martyn Farr.