Cave diving is definitely not for everyone, Martyn. What attracted you to it?

I was a keen caver and had been since I was about 10. Growing up in Wales there were lots of amazing caves, and after university when I got into ocean diving I thought I’d join the two together and start exploring the water I would come across when caving.

Did the danger aspect attract you?

Partially, but it’s not the danger element so much as the fact that so many caves simply end in water-filled barriers. The cave systems clearly continue beyond that point for goodness knows how far, and I had a burning desire to know what came next. Geologists had introduced dyes into a number of caves here in Wales and the dye could be seen emerging days or weeks later, often many miles away, so clearly there was a way through. I wanted to find out how.

What was your first dive like?

It was back in 1971 and there was very little information about cave diving at the time as so few people were doing it. It was very much learning as I went along, and I thought I was doing pretty well until my sixth dive, when I nearly died.

What happened?

I’d perhaps got a bit complacent, thinking I could explore new underground worlds by then, and I was at a place called Dan-yr-Ogof at the head of the Swansea Valley in Wales. There were three of us, and we’d already walked, crawled and climbed about a mile underground before I got in the water. The visibility was less than 2m – it’s not like the Maldives! – and the temperature was about eight degrees. You can’t really buddy up as you usually would when diving as it can all be a bit tight down there, so off I went on my own. I’d gone about 30m at a depth of 10m, breathed out, and when I went to take a breath in, the unimaginable happened: I couldn’t take an inhalation.

What did you do?

Well, the throat quickly starts to convulse when that happens, and what went through my head was total blind panic. I frantically tried to make my way out, got jammed, a minute passed and I started to breathe water. I’d seriously overstepped my mark and I was done for. One of my surface buddies noticed the pulls on the line – which we lay en route into the flooded passage in order to be able to find a way out when the water is muddied – came in and I somehow followed him back out. I was purple, coughing water, and the two people who were with me that day never went cave diving ever again.

But it obviously didn’t put you off…

No, it made me determined to make sure I learned all the skills I needed. A year later I was back at the same spot and went on to find a mile of undiscovered cave.

Was all of it underwater?

No, the submerged parts of cave systems are often just 50m or 100m or so. If you can navigate these, you often emerge at another – dry – cave. The passages that are filled with water basically link them all up.

Where are your favourite places to dive?

As well as Wales there are some magnificent caves in the south-west of France that I love to visit, but New Zealand is one of my favourite places and I’ve had many a great trip there. The first time I’d been invited by a friend who had been caving and found himself having to stop when the cave ended in water. I dived in and went on to find a mile of new cave. On one visit there I emerged after a dive in the most amazing cavern I’d ever seen – full of glittering stalactites and stalagmites. No one in the world had ever seen it. What’s incredible is that there are thousands of unseen caves like this all over the world – anywhere where there’s limestone rock will have them.

Are there any in the Middle East?

Some. I believe there may be some caves in Riyadh, but the place I would love to go to is Oman, where there are some fantastic caves.

What do you do when not cave diving?

Go caving! Cave diving is not a very sociable activity, whereas caving really is. One of the reasons I like to cave dive is that when you emerge at a new chamber, you can sometimes find a dry route back to another cave that is already known to cavers. In that sense it’s quite altruistic – I can sometimes extend the area that cavers can get to without them having to get wet.

The world’s deepest underwater cave was recently recorded in the Czech Republic. Does deep-diving appeal to you?

My specialisation is small, cold, murky tunnels that most other divers would stay well clear of. My goal is not to go deep; I’m looking for long, shallow systems where the margin of safety is a bit better. Things get exponentially more dangerous the deeper the water. But fear is part of the deal. Managing that fear is what is important.

What inspires you to lug your gear underground and step into freezing, black water now you’ve done it a thousand times?

I love it! It’s a wonderful activity, and the more preparation you put into it the better it will go. It’s really satisfying when you plan a dive and it goes exactly as planned.

Martyn runs both caving and cave-diving experiences and courses in Wales, France and Ireland. His new book The Darkness Beckons is out in April; go to