Try the seabed walk, " our tour manager told us. "They launched it in North Bay just a month ago - first time in India. " We were on holiday in the Andamans and had been debating whether to visit the North Bay island, 20 minutes from Port Blair - it was part of our package, but internet reviews had been discouraging and it seemed a better idea to head somewhere less touristy. However, the thought of traipsing about on the ocean floor was an intriguing one (we had friends who had done this in Thailand and Mauritius) so we flipped a coin and stuck with the original plan. It was the best decision of our trip.

North Bay itself is an unexceptional place - a small beach with a few stalls selling trinkets - but our attention was focused on the Sea Link Adventures pontoon anchored a little way off the coast;as we sped towards it in a small boat, we could see the tops of the nets that cordoned off the sea-walking area (roughly 400 sq m). On board, our instructor Babu gave us a five-minute briefing and confirmed that we were medically fit. (" No punctured eardrums, I hope?") What followed was nice and uncomplicated: dressed in our regular T-shirts and shorts, each of us climbed a little way down the ladder on the side of the pontoon, large oxygen helmets were placed over our heads and then, aided by a trained diver, we simply sank to a depth of around 20-25 feet.

Anyone who has been a few feet under water in the deep end of a swimming pool is unlikely to be spooked by this descent, but even nonswimmers feel disoriented for only a minute or so - after that, you're too busy gawking at the marine life around you. For a while after my feet hit the soft seabed, I thought the brilliant, black-and-yellow fish swimming a few inches from my face were cleverly manufactured optical illusions. I fancied I could even see slightly annoyed expressions on their faces!

Since everyone in our group was a novice, our guides were careful to keep us together, and much time was spent groping for hands to hold. But by the time we reached the coral beds, the minor discomforts of movement and being unable to verbally communicate were forgotten. We thrilled at the range of colours and the subtle movements of the coral tentacles, and kept our distance from a small, nasty-looking creature that seemed entirely made up of sharp teeth. Our divers photographed us with the bright orange clownfish - the stars of the animated film Finding Nemo - as they flitted in and out of their sea anemones.

Snorkelling and scuba-diving are terrific activities too, in different ways, but if I had to pick (on my limited experience), I'd give seabed walking a slight edge. It is - literally - more immersive than snorkelling (which doesn't involve going below the water's surface) and for the first-timer it's simpler than scuba-diving, because you don't have to stick a regulator on your face and practice breathing through the mouth. The only equipment you carry down with you is the helmet, which keeps your whole head dry and lets you breathe as you do on land. This means that once you've adjusted to the buoyancy and the otherworldliness of the setting, you can simply walk about and take in the sights.

The transcendent moment for me came when one of the divers took out a plastic packet and handed us clumps of mashed bread. Up to this point, the fish had been moving about serenely, content to look beautiful and regard us from a distance, but when the food appeared they formed schools and swarmed around us. I must have been a little late in letting go of the bread pieces because at one point I felt little mouths nibbling and sucking at my fingers. It was a little scary, but also exhilarating.

There's nothing like the ocean to show you how limited your perspective is. To go seabed walking is to be reminded that beneath the placid marine surface lies a whole new universe, one that a majority of humans never encounter. Coincidentally, a few days before going to the Andamans, I read Neil Shubin's book Your Inner Fish, about the discovery of an important piscine fossil - a creature that was among the first to attempt the shift from water to land millions of years ago. The book is a testament to the interconnectedness of all life, and I thought about it again when those fish were taking bread off my fingers. It felt like a fleeting brush with very distant cousins, on their own turf. I hope to visit them again sometime.

Seabed walking on North Bay is organised by Sea Link Adventures Cost: around Rs 2, 500 per person an extra Rs 500 if you want photos clicked - and that's highly recommended