Vern: If the best things in life are free, then night swimming off the dark end of West Railay beach is the best of those best things. Or at least in the Top 3. But I get ahead of myself.

A 5am start, a border crossing and eight hours in a cramped but modern minibus got us to pretty but busy Ao Nang beach in Krabi on Thailand's west coast. Tuk-tuks ferry sunburnt tourists to and from the edge of the yellow sand, where lady boys offer massages and other services. A dozen or so red and blue longboats are moored in the still blue-grey sea yet we are required to wait until demand swells to eight passengers before one will leave. When this happened we rolled up our shorts, hoisted our backpacks up high and waded out into the warm surf, then hurled our packs into the front of the long thin wooden vessel and clambered over the side.

Three to a bench we sat, low and close to the water, under a canopy. The motor looks homemade and there is no fibreglass case hiding the spinning cogs and belts. The small propeller is on the end of a long pole which the driver pivots to demand our direction. He hugs the coast which is a masterpiece of limestone cliffs worn into globular shapes by wind and water. Kayaks dip in and out of the shadows of overhangs and caves. Twenty minutes later he dropped anchor in the shallow water of the western side of the Railay peninsula. We were not on an island, but the mountain backdrop prevents getting there by car, so Railay has the feel of one.

It was overcast so the sea was still grey, but there was a slight green sheen in the folds of the ripples. The bay is small and neat, only slighty convex and guarded by two huge bush-capped obelisks, one on either end. Beyond the fine sand is a single pedestrian street lined with wooden restaurants and stores, otherwise all around are green mountains and grey cliffs. We followed a path to the other side of the peninsula and found the guesthouse said to have the cheapest rooms in Railay. Unfortunately, all the cheapies were full, so we reluctantly settled for an ensuite bungalow similarly priced to others on the island. The little log cabin was unfurnished but for a fan on the ceiling and a mattress on the floor. No window panes, just mosquito netting. Hey, we're not fussy. (Well we weren't fussy then. But later that night I had to kill and dispose of a cockroach so that Andrea would come inside, and after dark an unnerving scratching noise started from under the floor boards, so by morning we'd become a little fussed).

After settling in, we visited the Diamond Cave (at the halfway point on the east to west path) and its orange stalactites and fruit bats, then continued on to the beach where a large bottle of Chang beer and a banana pancake satiated us while the sun went down. It disappeared into swaths of cloud on the horizon turning them pastel blue and silhouetting the surrounding rock faces, while flame-twirlers laid out their poi and staffs and squeezy bottles of firelighter on mats, preparing for tonight's Fire Show.

Back on East Railay at The Last Bar we enjoyed some delicious Thai curries (coconut curry for me, green curry for Andrea - I won) and washed them down with a few more Changs and an indulgent cherry hookah. All the while, high tide lapped at the struts supporting the restaurant deck, flickering candles supplemented the starlight and a one-man-band covered Eagle Eye Cherry and other easy-listening hits.
Just after eleven, we decided to investigate whether a paragraph which caught my eye on the WikiTravel website was legitimate or a sneaky web prank. We changed into our swimsuits, picked up some towels and the dive mask and navigated back across to West Railay, which is without bars and was now dark and deserted.

I stripped down, strapped on the goggles and slowly waded into the silky black water, "Wait on the beach," I yelled back to Andrea, who I couldn't see anymore, "there's no point us both getting wet if nothing happens." I dived into the shallow water, opened my eyes and couldn't believe what I was looking at. I burst back to the surface and shouted, "It works, it definitely works! Come, come!"
I then threw myself back into the water and thrashed around. Through the little plastic window in front of my eyes I watched myself turn into a human comet. Orbs of bright green light dripped off of my arms and legs and beamed with fury for a few seconds before fading and dispersing. My limbs were wreathed in twinkling fairy-lights which doubled and tripled in quantity and brightness when I moved and faded when I stilled. Andrea found me easily, splashing loudly and emitting a blue halo. "From above the water you look like a super hero or something, like the Human Torch" she said looking down over me. I handed over the mask and Andrea put it on and hurled herself into sea instantly creating around her a flurry of constellations.

Apparently the water contains bioluminescence, an invisible algae or plankton microbe which when agitated emits a brilliant light, and thus disturbed water lights up like a Oxford Street at Christmas time. It is a mindbending phenomenon and as Andrea said as she popped up out of the water, "well that's an instant Highlight for our list." Andrea found that by pushing off the bottom and pulling back the water with a breaststroke movement, she could create a vortex and the phosphorescent orbs would stream past her face, like the Windows 95 'Space' screensaver, or like entering Hyper Space. I copied her routine and it was fantastic. I really felt like a deity floating through the galaxy and creating stars with the wave of my hand where before there was nothing.

We exhausted ourselves splashing about and passing the mask between us and finally decided it was time to get out. Drying off on the beach we were buzzing with excitement and were bursting to tell everyone what we'd just experienced. "Why were we the only ones in the sea?!" "Why wasn't it full of people." Some drunk Germans appeared out of the shadows. "Are you going in?" Andrea asked thrilled at the prospect of sharing this experience with someone. But no, they weren't. They had walked round the cliffs at low tide from the next beach over, Tonsai, but now that it was high tide they had to climb over a mountain called the Sleeping Indian in the dark, to return to their accommodation. They were probably right to be grumpy but nothing could rain on our parade!

The next morning after breakfast and fruitshakes we walked past the mangroves of East Railay and down a path cut through the jungle and rock to Phra Nang beach. Well fed monkeys hanging off of a bough which stretched over the path greeted us noisily. The beach, one of the world's 10 best, (travel writers sure do like a numbered list!) was small and crowded (so travel readers must like 'em too). The sea is light green, shallow and warm and floating in it, scattered all the way to the horizon, are large tree-covered domes. Behind the beach, climbers hang off the limestone cliffs like ants struggling up a mound of melted candle wax. To the left is Princess Cave, a cavern in which the locals believe a princess lives who controls the fertility of the sea. To guarantee a big catch fisherman leave red tipped wooden phalluses here and the rude pile now nearly reaches the cave's ceiling. Andrea mused that an inverse offering might please a male deity but assured me that if there is a Sea Princess in there, the fisherman are doing themselves no favours littering her porch with obscene sculptures!
We read and swam and explored some caves with the hundreds of other beach-goers until it started to drizzle and most people called it a day. But we waited it out in the shelter of a cave watching the mountaineers on the cliffs with their ropes and the mad local free-climbers on the cliffs without their ropes. After the rain dried up, the beach was much quieter and we stayed until the early evening. As the tide snuck away, the heavily eroded sub-aquatic bases of the islands were revealed and rather amazingly it became apparent that those mighty monoliths are balancing on fragile mushroom stems. But then aren't we all.