IT GETS DRUMMED INTO YOU as you learn to dive - never, ever hold your breath. But sometimes, its impossible not to.
Wed flown from London to Los Angeles, Los Angeles to San Jose del Cabo on the Mexican Baja Peninsula, driven to Cabo San Lucas, then sailed due south for more than 24 hours.
We finally hit the water at San Benedicto Island and swam around a pinnacle of rock known as the Boiler. And there, right in front of us, nose to nose, was a giant Pacific manta ray.
This was why wed trekked to the Socorro Islands, and she was absolutely, utterly, breathtaking.
We froze, terrified that the slightest move, the smallest bubble would scare this 7m marine giant away. But we were mistaken. The manta waited too, hovering motionless for what seemed like ages before, turning slightly, she reassessed the situation - and us - and approached.
We breathed out (as we simply had to by then) and she slid over our heads, allowing our exhaust bubbles to trickle across her tummy. OK! We realised that it was a game.
We exhaled more bubbles. She swept off and came back, we laughed again and she repeated the manoeuvre. The rest of the dive group arrived, but not a single person diverted her from the game.

THERE ARE FEW PLACES on the planet where you can have an experience like this. Other destinations are renowned for their manta populations, and justifiably so, but nowhere else delivers such incredible interactions with them.
It was an encounter that would occur almost daily, and one that wasnt limited to the mantas. Over the following days, we were to discover just how many marine animals in this region are equally friendly and curious.
The Isla Revillagigedo archipelago consists of four specks of land: San Benedicto, Socorro, Roca Partida and the rarely dived Clarion. Each is the tip of an ancient volcano sitting on the edge of the Pacific Ring of Fire.
Often nicknamed the mini-Galapagos, the landscapes of both island groups are similar. The Revillagigedo land animals are less distinctive; there are many indigenous species, but you wont get to see them, as no one is allowed on land.
The marine life is also closely aligned to that of the Galapagos. Five different shark species are seen regularly, along with the mantas, dolphins, whales and many fish indicative of the region.
We were travelling on Nautilus Explorer. Our floating home was a large and stable vessel, which was important, because the run down to the islands is quite a haul over open seas. Compact cabins and a comfortable lounge area allowed us to fill the time socialising until we arrived, full of anticipation.
That first dive at San Benedicto was incredible, and we wondered how it could get any better.
However, Sten and Buzz, our divemasters, threw us straight back in the water at the Boiler and, trying to remain calm, we headed around the pinnacle again.
The rocky terrain was interesting - we spotted fish and morays we had never seen, even a few sharks in the water column beneath us - but who cared
The manta was waiting for us in exactly the same position, and right behind her was another.
We were forced to move away from this impossibly perfect experience as the wind picked up, and we relocated to a small bay beneath a lava flow that had scorched the island some years before.
The topography was gentler, with large, tumbled rocks creating swim-throughs in the shallows.
We spotted a green turtle as we rolled in, but within milliseconds another manta arrived. This lady was completely black, unlike the ones earlier, which had been marked by pale chevron patterns.
In the fading afternoon light, she appeared like a sleek Stealth bomber doing a recce over the bay. Several juveniles arrived with her, but they stayed back until the adult led them past, following her in perfect formation.
Meanwhile, we had relaxed enough to start noting the rest of the marine life: redtail triggerfish arrived en masse, there were spotted boxfish, some of the biggest scorpionfish we have ever seen, and we were introduced to the indigenous Clarion angelfish and Clarion damselfish.

NEXT, WE WERE OFF TO SOCORRO, the largest island in the group. After checking in at the naval station, the only community on these islands, we transferred to Cabo Pearce on the eastern coast.
The divemasters amused themselves by waxing lyrical about how the ripping currents attract numerous sharks, then watching the divers race to be on the first RIB. By the time we dropped in the currents were minimal and the sharks non-existent, but we werent disappointed, because another two manta rays came sliding in.
This time, we could see that one was a male, evidently the first the crew had seen for some time.
We headed back along a promontory of rounded rocks and found an octopus with a similar attitude to the mantas.
Far more interested in creeping towards us than away down a hole, he slipped and slithered, extending a tentacle to touch a hand or camera before moving on to check out the next diver. We lost sight of him only when we were mobbed by a mega-school of redtail triggerfish.
Cabo Pearce lies beneath a striking rock wall, creating a sculptural backdrop to our moored vessel. As the sun went down, Sten dropped another bit of tantalising news into a dive brief. After dinner, would we like to go snorkelling with the silky sharks Naturally, he was met with a dumbfounded silence.
The story went that, after sunset, light from the boat would lure flying fish to hunt across the surface, and that attracts the silkies. Everyone was invited to drop in off the rear deck, with strict instructions to stay close to the hull.
At more than 3m long, these elegant predators swooped around and under the boat, curiously watching the divers.
It was hard to see them well, however - apart from all our excited buddies getting in the way, the light attracted a lot of plankton and worms.

AT PUNTA TOSCA, ON SOCORROS WEST COAST, we found another submerged rocky tongue, with several diverse sections of reef to explore.
One was an almost vertical wall of rock slabs, stacked on top of one another like some ancient Aztec fortress. They were covered in small green sponges and tiny feathery corals, legions of lobsters and untold giant hawkfish.
We found large grey rays and a guitarfish; we could even hear whale song reverberating through the sea, though we never did see them beneath the waves, a terrible tease in our minds.
On the other side of the ridge and closer to shore, large tumbled boulders had created a maze of caverns.
A green turtle was resting in one, and stayed completely still, posing for cameras and videos until a lobster raced right up to his rear leg, nipped at it, then hightailed it out of the cave, followed by the irritated turtle.
After another overnight sail, we arrived at our final stop, Roca Partida. The smallest, most barren island in the group, this exposed twin pinnacle of rock erupts from the ocean. At 100m long and much less wide, beneath the surface it falls equally dramatically down to the depths of the Pacific.
We awoke to see humpback whales all around - they were a way off, but staring in any direction for more than a few minutes would reveal a waterspout or fluke breaking the surface.
Wondering just how much more exciting this trip could get, we hopped into the RIB and motored to where we could see a pod of bottlenose dolphins.
Hardly daring to hope they would stay, we rolled backwards, straight into the pod.
Again stunned into breath-hold, we watched one a few metres away. Motionless and perfectly vertical, he waited for us to get organised, then flipped his tail, did a ring around his gang of six and came back.
He paused, swam off a few metres, stopped, waited and looked. We noted the request to play, finning cautiously in his wake. He glanced back as if to say hurry up, so we took off after him.
This one cheeky dolphin continually turned to check on us, even dropping below and rotating his tummy up, like a puppy asking for a scratch.
Not surprisingly, we lost track of the time and our depth - we paused only when the visibility suddenly dropped, and our computers indicated that we were at well over 40m!

ITS POSSIBLE TO CIRCUMNAVIGATE ROCA PARTIDA in a single dive, but we never did this, as there was a creature on every surface, and always something in the blue waiting to be admired.
On the northern tip at depth, silvertip, hammerhead and Galápagos sharks were seen on every dive. They were rarely close, but every now and then one would peel away from the rest and swoop in to inspect us.
We nearly had a head-on collision with a Galapagos shark as we looked up from inspecting the cracks and crevices on the walls. There were juvenile leather bass, the Panamic fang blenny, minute rainbow scorpionfish and sally lightfoot crabs. It was frustrating that, just as we would spot an unusual small creature, another manta would appear and wed have to desert the rest.
Later, we would return to the walls, where several wide shelves were stacked with whitetip sharks.
Of all the up-close encounters we had, these were the most unusual. Small caves would be packed to bursting with up to a dozen juvenile whitetips. A few feet away, two more would be nestled into a crack with a giant green moray.
The moray appeared to be acting as a surrogate mother, keeping the young sharks cosy by wrapping her sinuous body around them, while on a nearby shelf, stacks of older whitetips would number four or five deep.
They would watch us approach, lift off into the blue, then return, rotating to face forward to pose for a photo.
Where the Islas Revillagigedo differ so much from other destinations is that the diving is all about interaction. Mantas, dolphins and sharks were all as curious about us as we were about them.
Was it all a daydream No - we did breathe long enough to take pictures and notes. No one really knows why, but this is one place where the resident pelagics are receptive to humans. Take a deep breath - youre going to need it.

Brits Beth & Shaun Tierney are co-authors of this Footprint book, a popular travel guide first published in 2006 and recently updated.
The new edition of this chunky 360-page book covers 220 popular sites in 19 countries, all of which have been reviewed and photographed by the Tierneys, and given star ratings.
Also included are both regional and dive site maps, biodiversity charts and dive data tables, and personal recommendations for operators, dive centres, liveaboards and for
non-diving pursuits.
Beth & Shaun Tierney are also authors of the companion Footprint guide, Dive Southeast Asia.
ISBN: 9781906098766
Softback, £19.99