WE PEER INTO the rocky cleft, and the clear water gloops soporifically. The light breeze is from the east; today the conditions are perfect. At the back of the fissure there is little to suggest anything unusual, yet this little-known, discreet recess in the bare-rock slope is the entry point to an enchanting submerged cave: Seal Hole.
Here, at Prussia Cove, near Rosudgeon in south Cornwall, is a veritable gem of a British cavern.
It’s an easy, shallow shore dive that leads for 50m through the rock to emerge at a smaller opening to the west.
Just inside the entrance, the passage size enlarges to perhaps 2-3m in diameter, while the depth remains no greater than 3-4m. As a taster of UK cavern and cave-diving, this is
a perfect venue.
As with any tunnel the light level falls away surprisingly fast, and laying a line here is strongly advised – 50m may not sound very long, but as there’s a short but blindside tunnel to the right-hand side, and the likelihood of organic detritus on the floor, the place generates a real feeling of dark adventure…
“Where in the UK can we go to dive in caverns” is something I am asked regularly on my training courses. Unlike Florida or Mexico, Britain is not renowned for its recreational cavern- and cave-diving activities, but discerning researchers will quickly discover that there are any number of places that present a wide variety of cavern-diving at a basic, easily accessible level.
There are numerous submarine caverns and swim-throughs along our coasts, and there are some eminently suitable limestone caves, tunnels and mines inland.
The following sample of sites will prove a very interesting change to a day’s activity under water, and whet the appetite of all abilities.

AS WITH ANY ACTIVITY involving wrecks, those taking their first tentative steps into the exciting world of overhead-environment diving will need to consider carefully their training and experience.
Likewise, it is fundamental that, as with any scuba activity, cavern sites should be selected with due regard to weather and water conditions. My new book addresses these and many more issues in a user-friendly way.
Not too far from Prussia Cove, close to the Lizard, lies Kynance Cove. Weather and water conditions are crucially important here.
Winds from the south-west generate swell, and the best advice at these times is to forget this site altogether.
It’s a bit of a trek from the car park to the small bay with its summer cafeteria, but in good conditions the submarine tunnel that passes for 50m beneath Asparagus Island is really sporting – definitely a UK classic.
If the day’s diving is being undertaken from the shore, the optimum time to dive is at low tide. There are no side leads here, just a spacious tunnel with coarse clean sand on the floor, and
a profusion of colourful marine life clinging to the walls.
While it is possible to circumnavigate the whole of Asparagus Island in an anti-clockwise direction on a 12-litre cylinder, do not venture into the second, shorter, cavern on the seaward side of the island.
This presents a direct connection with the notorious Kynance Cove “blowhole” – a site to avoid!
There are undoubtedly many more exciting caverns to dive in Cornwall, especially at high tide. Boscastle, for example, has a notoriously dramatic blowhole associated with a 50m-long tunnel through a headland, but this is rarely dived because of the fickle nature of the environment.

HERE ARE SOME other sea-diving opportunities in England and Wales:
Up at St Abbs, in the North-east, lies Tye’s Tunnel, an interesting 15m-long swim-through approached as a boat-dive.
Down in south Devon there is a swim-through at Babbacombe, near Torquay, and other caverns at Watcombe Head, just a few miles further east.
There are short caverns off both north and south Pembrokeshire, the Llyn Peninsula, Anglesey, Llandudno and at the southern tip of the Isle of Man.
Scotland again has many short caverns, but perhaps the best-known and undoubtedly the most dramatic and challenging would be those at St Kilda.
Setting aside the extraordinary difficulties of access at St Kilda, the remainder are all sites where divers of virtually every level can enjoy a great recreational experience – something refreshingly different.
The inland cavern sites of the UK and Ireland are substantially different in nature to those in the submarine realm. Depending on season, water temperatures here vary between 6 and 18°C. These caves may not host the same wealth of aquatic life as marine sites, but certainly in fresh water environments the diver will encounter interesting life-forms and view some weird and wonderful rock-sculpting.
Under low flow conditions, for example, the cavern-diving at two locations in Porth yr Ogof Caves, south Wales, presents a unique experience to all comers. Here there are bare surfaces smoothed, indeed almost polished, by the relentless action of water over tens
of thousands of years.
These two sites are just 4m deep. Under water there are trout and bullheads in profusion, while in the airspace overhead are some attractive displays of stalactites and stalagmites. This cave, in the middle of the Brecon Beacons National Park, presents a unique day out, with the added interest of a gentle wander through easy-walking cave passageways to round the day off.

TUNNELS AND MINES
Scattered across the UK are many different types of tunnel and mine. Places such as Vobster Quay in Somerset and Dorothea in north Wales are renowned dive-sites with well-known swim-throughs. These short, spacious passages, originally connecting parts of the quarry workings, are routinely passed through by divers, and will add spice to any dive.
But mines, in particular, must always be treated with added caution and respect. Relatively few are deemed suitable for cavern-diving. Appropriate training should be undertaken and local advice sought prior to a visit.
In Scotland, Roscobie limestone mine in Fife is a prime northern venue. As this is an “open” water site, in a flooded stone quarry, temperature and visibility in the surface lake varies according to season.
In the summer an algal bloom is a little disconcerting in the environs of the multiple, interconnecting entrances, but this site will provide a fine cavern experience, provided that one remains within the daylight zone.

SOUTH OF THE BORDER, Hodge Close Slate Mine, near Coniston in the Lake District, is another popular site at any time of the year.
Given that the main tunnel here is accessed at 25m depth and the water is generally cold (6° or less), visitors would be prudent to consider their level of training before embarking on anything other than the shortest of penetrations.
Another superb but much shallower site is Holme Bank Chert Mine at Bakewell in Derbyshire. But by far the finest mine diving site in the UK as a whole is the Dinas Silica Mine at the head of the Neath Valley, in South Wales.
It’s a 600m walk to reach the entrance, followed by a further short walk underground to gain the water. Water clarity is stunning; visibility is generally well in excess of 25m.
It’s a veritable labyrinth of safe and spacious tunnels, leading to a maximum depth of 23m.
Cavern-diving is an achievable objective for the majority of divers.
This type of diving does however require awareness and respect, which follows naturally from the right attitude, training and experience.
While sites in this article have been selected on grounds of general suitability and access, it is stressed that if you visit any of these places your dive objectives must be appropriate, both to the level and type of training received.
All the necessary information relating to location and access, a brief history of exploration and practical comment on appropriate equipment for these and many other sites throughout Europe, can be found in Classic Darksite Diving.

WHAT IS CAVERN DIVING
Cavern-dive training is the general foundation upon which all subsequent activities in caves and mines is based. Cavern-diving is not cave-diving; it is a very basic introduction to overhead-environment diving, involving penetration of a cave or mine but only for a limited distance, to a limited depth.
Deep sites and decompression are held to be outside the scope of this type of diving.
This foundation certification does not involve any restrictions or “squeezes” (at all times it is possible for two divers to swim side by side, or one above the other) and complex sites should be avoided.
The maximum penetration from air surface is 60m, and this distance should be reduced on consideration of depth, passage-size and visibility. Plan the dive and dive the plan.

POINTS TO NOTE
Some dive sites require line; some do not. If you’re going more than a few metres into a cavern, remember that a line should always be used.
Always consider the possibility that previous visitors may have abandoned line at the site and that broken line, in particular thin technical line, is especially hazardous (4-6mm nylon line is recommended in UK environments).
Remember that cavern-diving was originally conceived as a daylight activity; as such, avoid entering these places at dusk or in low light levels.
Lastly: the recent upsurge of interest in side-mounting is an worthwhile and healthy development, but an open-water side-mount course is not a substitute for specific training
in cavern- and cave-diving.
MARTYN FARR’S NEW BOOK Classic Darksite Diving selects sites in Britain and elsewhere in Europe that are relatively “easy” to dive; places people may visit to extend the range of their recreational cavern, cave- and mine-diving experience.
The book is a companion volume to Martyn’s Diving In Darkness, the 2003 global introduction to overhead-environment diving.
Classic Darksite Diving is lavishly illustrated, with all the practical information needed to help you plan some spectacular diving. It is published by Wild Places Publishing, 192pp, ISBN: 9780952670186, £27.50.