Despite its majestic presence at the gateway to the Mediterranean, the Rock of Gibraltar is still a very small spot on the map. Though named in legend as one of the twin Pillars of Hercules, it is barely 6km long, and despite the pace of land reclamation on its western shore, there is not much room for its 30,000 inhabitants.
It is not surprising, therefore, that some visitors find it hard to occupy themselves there for more than a few days. After all, once you have been to the top of the Rock, walked or driven round it, and seen the historical sights, what else is there to do
Fortunately, for divers, the answer is simple. In the waters surrounding Gibraltar there is much to explore: an abundance of wrecks, drop-offs, and a blend of Atlantic and Mediterranean sea life unique to that part of the world. Some of these attractions were featured in the January edition of Diver, but for those with the right contacts and the wish for something different, there is an alternative. It is a dive inside the Rock.
As most visitors to Gibraltar soon discover, the Rock is anything but solid. For the past 200 years or more, military engineers have dug and burrowed ceaselessly into its limestone heart, creating more miles of road within the Rock than presently exist without. This man-made labyrinth, constructed on a variety of levels, combines intimately with the Rocks own vast natural system of fissures, tunnels and caverns to form a veritable honeycomb inside it. Gibraltar is, in fact, a massive, rock-hard sponge. There must have been many times during Gibraltars military history when engineers tunnelling into it came across these natural caverns by chance. But few such finds would have been as dramatic as a discovery made at the turn of the century near Ragged Staff Gate, a portal in the towns old defensive wall.
On either side of a tunnel deep inside the Rock, a series of huge chambers was being dug to accommodate purpose-built ammunition magazines. When the smoke and dust had cleared after blasting inside one of these, it was seen that the back wall had been blown outwards into the inky blackness of a huge natural grotto.
It must have been with some trepidation that the workforce - probably ordinary soldiers - ventured forward with lamps into this previously sealed place where man had never before set foot. From the newly blasted opening they would have picked their way down a steep rubble slope into a high-roofed, lozenge-shaped cavern in which stalagmites and stalactites of various sizes could be seen. But it was among the rocks at the foot of this slope that the most interesting discovery awaited them. There, stretching away into the darkness, was a deep pool of the clearest water imaginable. No one now seems able to say for sure who was the first to explore this pool, or when the first dives were made. What is certain is that to dive the Ragged Staff Pool today is still as memorable an experience as it was for those first privileged few. For the pool is not just a simple water-filled hole; it is the entrance to an enormous flooded cavern deep within Gibraltars living rock. Diving here requires clearance from the Ministry of Defence.
From the outset the most striking thing about this place is the astonishing clarity of the water: it makes an immediate and powerful impression the moment you duck your head beneath the surface. Torch beams illuminate no suspended particles whatsoever, but instead lance cleanly through the water to pick out impossibly distant objects.
The water is so transparent that to swim gently downwards is to fly; but for the familiar bursts of bubbles there is no sensation of being underwater at all. Even the taste of it, like air, is neutral, because initially the water is fresh, not salt.
Three fixed lines to different destinations lead the way down, and as you make your way along one of these through the flooded entrance passage, so the first stalagmites begin to appear along the floor. They look like a scattering of Stone Age traffic cones as the torch beams pick them out. Directly overhead hang their fragile, icicle-like counterparts, their downward growth now stopped forever by the floodwater.
At the far end of the entrance passage stands the single most impressive geological feature of the entire cavern: a solid white pillar joining floor to ceiling. It is a marriage of stalactite to stalagmite, the work of thousands of years of dripping water during the caverns dry period.
What was going on in the world outside when stalactite and stalagmite first touched, fused and began forming this solid white column in Ragged Staff Cavern Was Stonehenge yet to be built Was Rome still a village
Passing this column, you leave the entrance passage behind and start out into the main chamber. As you descend, so the bottom drops away, the walls retreat, the ceiling lifts to greater heights, and the fixed line leads you out into mid-water.
A probing torch beam reveals distant rock faces, giving the impression of great spaciousness, of room to swim and explore. To the left and right the two other fixed lines can be seen fanning out towards their separate destinations at 20m and 30m respectively, while the central one angles steadily downwards into darkness, pointing the way to the bottom.
Suddenly, everything in the torch beam becomes blurred and unfocused; instruments are impossible to read and hand signals are passed through a strange wobbly haze. This is the halocline, the division between fresh and salt water we were briefed to expect at this point. We pause to enjoy its visual effects for a moment before adjusting our buoyancy and continuing the descent.
Almost at once we pick out the bottom in the distance and arrive there after a last long glide down the line. Following this line all the way, we find it has been tied off round a miniature version of the pillar at the entrance passage. Our computers show 41m.
Even here at the caverns deepest point there is still a lot of room to move around and explore. Boulders and sharp-edged rocks lie tumbled about, all with a generous coating of brown silt over them. We tiptoe around on our fingers, keeping fins as still as possible and well out of the way. There are cave-like hollows in the walls, deep fissures, and piles of sharply splintered rock strewn about as if blasting has just taken place. It is a strange and fascinating place.
For the ascent, which comes all too soon, we transfer to the 30m fixed line for a closer look at the walls. They are a complex mixture of angular faces and overhangs, festooned with drooping icicles of stone, strongly reminiscent of the Titanics famous rusticles. These appear wherever water dribbled or dripped in ancient times, adding a touch of the exotic to this already mysterious and silent place. One or two small tunnels also exist within the walls, leading perhaps to other caverns or cave complexes, or to nowhere at all. Too narrow to be investigated without specialist techniques and equipment, they have not so far been explored. We pause only to shine our torches into one of them and wonder where it might go.
Soon the stalagmite-stalactite column reappears ahead of us, this time framed in a luminous halo of greenish light from the arc-lights in the dry cavern above. We take the opportunity to have a last look at it before gliding past on our way back to the surface. Already we are envious of those whose turn it is to dive next.

  • For information on getting clearance to dive the Ragged Staff Pool contact the local BSAC branch in Gibraltar.