Small service tunnels and ventilation shafts connect enormous mining chambers in the 270m-deep Ojamolimestone mine.
T IS JUST TURNING DAYLIGHT as we arrive at the gates. The heavy padlock is frozen, which is perhaps to be expected at -6C. I am thankful that this is the warmest winter on record in Finland, as Klaus, my host, informs me that it can fall to -20C at this time.
I am more than a little apprehensive as we drive to the waters edge and the small Portakabin that serves as the divers warmhouse.
Thankfully the heating is on, and heavy coats can be removed. Outside the huge lake is frozen solid with steel ice - just a couple of inches thick, but enough to need sawing with a special set of ice-tools, to permit entry to the water.
Today is Sunday, and yesterday saw Finlands first technical dive conference. Some 260 people had turned up for this extremely well-organised event. I had been invited to speak. Luckily most of the audience could understand a fair amount of English.
But that was yesterday, and today I had accepted the invitation of an ice-dive into Finlands most popular dive site, the Ojamo mine on the outskirts of the small town of Lohja.
This site has become the base for the Finnish Cave Diving Association, a hardy bunch of enthusiasts who for most of the year are mine-divers, as they have no flooded natural caves in their country.
But this is no ordinary mine. In the annals of mining history, it has international importance. Many, many kilometres of tunnels stretch out from beneath the frozen lake, all in water ranging from freezing point at the surface to 4C (the all-year temperature) below 6m depth.
My guide Klaus Berghem and Matti Anttila had set the current limit of penetration of 150m at the site on a dive lasting the best part of four hours.
Clearly exploratory dives into the deeper water needed to be undertaken
in the summer months, when surface waters might reach 20C - essential warmth for the long periods of deco.
The guys had fitted me out with all the kit I would need for an hours dive to the 40m level. I had a pair of 10-litre cylinders filled with trimix, and a small bottle of argon for suit inflation.
Diving humour is the same the world over, and most of the gathering was cynical about my 5mm wet gloves. Everyone here wears dry gloves.
I felt like a Michelin Man, and my eyes were watering like a tap in the stiff breeze. Outside, a dozen or so people were quietly gearing up to dive the upper levels of the mine. I was extremely impressed by the organisation and efficiency of all concerned. Small teams discussed their dive plan in the warm house, and then it was back into the excruciating cold, with 40 minutes or so of even greater cold to come.
As there is no global uniformity on mine diving standards, the Finns have set up their own system to preserve an exemplary record of safety.
While scuba divers can be accommodated in the huge expanse of open water (open meaning when its not frozen!) more rigorous requirements are necessary beneath ice and deep inside the mine tunnels.
Here a tally of some 25 dives is stipulated in the shallowest of the tunnels, at 28m, before being allowed into the next level at 40m.
I was privileged. Klaus Berghem and Perry Sujoki were taking me to the deeper section, named Marioworld.
My guides had been my cave students in the UK back in 2000, but today I felt a clear role-reversal!

I QUIETLY GOT MYSELF ORGANISED, dreading getting into the water to find a leak or some other embarrassing setback. The guys had gone to so much trouble to set this dive up, and had even borrowed flashguns from a fellow-photographer on my behalf.
There was limited room in the small icy pool and, moving to one side to make more space, Klaus cut and punctured a dry glove on the sharp edge of the ice.
A replacement was almost instantly made available. There was no fazing these guys.
The Inspiration rebreathers they were both using were apparently prone to freezing up in these temperatures, and my Poseidon did just this shortly after I got into the water.
Dipping below the surface remedied the problem in a few seconds, and it was with some relief that the dive began and we dipped away into the murky water of the lake. The steep descent began.
At 40m we turned momentarily through a much smaller roofed section, then immediately out and over a vast chasm. In the misty, murky algal-bloom water, there was no way of picking out structural features, or trying to make sense of passage proportion.
Yes, there was a line close to a right-hand wall but, beyond that, the place was an empty void in all directions.
For the next 50m or so it was the memory bank formed by the dive briefing that made sense of the place.
I remembered that there was a roof somewhere 20m overhead and, perhaps most soberingly, a floor of sorts somewhere down at a depth of 78m. Buoyancy problems were not an option.
People might be more concerned by a regulator malfunction or loss of gas in such an environment, but this was not an overriding issue as redundant gas was plentiful. Because they dive here so regularly, the teams have installed a spare bottle at depth for just that eventuality. Getting lost in such a place is possible, but the lines were fitted with directional arrows, so provided one stayed with the line, there were no worries on that score.
The major concern was that of a torn drysuit. Hypothermia would be near-instant. Reassuringly, my fingers worked well and, with a good percentage of helium in the mix, operating the camera was fine.
Soon reassuring rocky walls, roof and floor appeared. Marioworld was the sort of place where I could return to my comfort zone, where at last the water was crystal-clear.
I marvelled at the workings, and wished now that I had been better prepared and with time to see more.

THE DAY BEFORE, we had been given an excellent overview of the mines history by Klauss deep-diving partner. The Ojamo mine had been working right up to 1965, so there were full records, photographs and surveys of the place.
The mine is set in limestone rock, a rare commodity in itself in Finland, a country notably short on mineral resources. Small-scale extraction had been undertaken from the 1500s, but it wasnt until 1925 that production took off. Deposits of limestone were limited, and simple geology dictated that the mine drove ever deeper to win the rock as cheaply as possible.
Levels were driven at 28, 40, 58, 88 and 138m, and by the end of the mines life the tunnels were chasing the reserves down at 238m.
Work was hard and air quality bad. Much of the mine was driven out beneath a local lake, and at one point the mining extended accidentally and critically upward to such a height that the roof was just a few metres below the bed of the lake.
It was a miracle that the thin section of rock took the strain. A breach would almost certainly have cost the lives of up to 200 men and ruined the mine. A huge concrete wall was erected to redress the worry, and the work continued on down.
All manner of artefacts can be found in the tunnels. I wondered what the Russian prisoners of war in the 1940s and other enforced Finnish convict labour in the years to follow would think of the fact that this place is now Finlands premier recreational diving attraction.
All too soon, the dive was turned and the fun began! I had misjudged my weighting on entry to the water and now, with depleted gas, I was kilos lighter.
As the ascent from 40m began, so did my embarrassment.
It is a golden rule that one should never pull on the line, but this soon became my only resort in the face of inexorable upward momentum.
Fortunately the Finns had foreseen such an eventuality. A stout line had been installed here to offset the much greater embarrassment that would result following a premature ascent.
Only at 6m could the situation be adequately addressed, when I got a tree trunk firmly gripped between my thighs and quietly squeezed every last bit of gas out of the suit.
With buoyancy and trim restored, the computer screen eventually cleared.
An hour earlier, the sky had been clear. Now the wind was driving cloudy skies and snow, but the diving was still going on. I was warm and happy - despite my shortcomings with buoyancy, there was a great sense of achievement and satisfaction. I had done what I had come to do, and now I could really feel the pulse of the area.
Only by diving can one thoroughly appreciate the environment for what it is. We all know there is only one Red Sea and that the cenotes of the Yucatan are like nothing else, and here today I had gained that special insight to the extreme nature of the mine diving in Finland.
I knew the Finns were a hardy race but after diving with them I felt far greater respect. The mine diving at Ojamo is without question among the most challenging and extreme on Earth.

Photographer Sten Stockmann describes one of the dives he undertakes regularly in the Ojama mine.

MY TANKS SCRAPE THE CEILING and my chest is pressed to the white limestone floor as I squeeze through the restriction with my scooter in front of me. Putting my heels to the ceiling, I push myself through the restriction and emerge just below the roof in an enormous hall.
Visibility is more than the 30m that my HID light can illuminate. My buddy emerges from the restriction engulfed in a white cloud, and we hit the scooter trigger and start gliding over the apparently floorless room.
At the end of the hall lies an old stairway leading 20m down to another hall. Descending headfirst with electrical wires and light bulbs hanging from the ceiling is a bit tricky, but we avoid entanglement, and soon emerge into the next chamber.
The water here appears even clearer. We are now at the 58m level, and as we scooter across, we admire the reflections of our lights in the bubbles trapped in the ceiling from previous dives.
My eyes follow vertical walls that seem to drop forever, and I try to make out the floor which should be at 88m, some 30m below us, but apparently my light is not strong enough.
As we exit this room we turn left, round an enormous pillar and head for a brick wall with a small opening. On the way we pass an old wooden dynamite box, with some sticks still left in it.
As we pass through the small hole in the brick wall the water starts to get greener, and visibility deteriorates. Ascending a slope of rocks and stone, we soon find natural light above us. We are now in the open quarry part of the mine, and as we continue towards our decompression bottles we pass some old trees with leaves still in place.
And if you look closely, you can find crayfish and small perch hiding under the rocks. Decompression is uneventful, and soon we are back in the sunlight.
Martyn Farr
Breaking the ice - Klaus Berghem and Martyn Farr.
Following a mine tunnel at 40m.
A diver scoots past an old stairway.
Examining fuse/circuit breakers near the main elevator shaft.
The open- quarry part of the mine, at the end of the day. The quarry is used by a commercial diving school and an offshore safety-training centre. Authorised diving activities are arranged every week, all year round. year around.
Cold but content.
Sten Stockmann