If you like to get on down, try canyoning in Spain

Abseiling down waterfalls and clambering through tropical jungle were no problem, but the snake-bite kit had Damon Coulter a little concerned

Henry runs through the safety equipment spread out before us. The ropes and climbing gear look familiar. But the rescue kit is a strange collection of expansion bolts, complicated descenders and snake-bite syringes. It has me asking slightly worried questions about poisonous snakes, flash floods and general escape plans. When Henry is happy that I understand everything, particularly and pointedly the fact that there is no escape plan, each item is put into a watertight container and then into a small plastic rucksack. That will, in turn, sit on my back on top of several layers of thick neoprene.

"Don't worry," laughs Henry as he sees me struggling to get into my wetsuit jacket, "it'll get more comfortable when it gets wet."

Poisonous snakes aside, it is getting wet that I am perhaps dreading most. At 1,500m above the town of Almunecar on Spain's Costa Tropical, it's a little late to realise that there are reasons I'd never been canyoning before – not being able to swim being a particularly good one.

The Costa Tropical, an hour's drive east of Malaga, offers a distinctly different experience from the rest of the overdeveloped Costa del Sol. Winding our way high into the mountains that morning, we had passed Moorish villages and Roman aqueducts surrounded by terraced hillsides on which orchards of custard apples, avocados and even bananas grew. It was vastly different from the concrete resorts. It is a distinction that even the resort towns of the coast are keen to preserve, as they pursue adventure-seekers. Skiing, climbing, hiking and watersports feature on the list of local attractions, but it was canyoning, still a relatively new sport in this area of Spain, that I had come to try.

Canyoning is basically a kind of above-ground caving that uses a combination of abseiling, swimming, sliding and jumping to descend some of the steepest and narrowest of river gorges. Our chosen canyon was the Barranco de Madronales, which is a tributary of the more popular Rio Verdi. It wasn't perhaps the easiest route in the area, being both steep and technical (a descent of more than 800m in height in just over 3km of length) but it was much dryer than most. Difficult abseils I didn't mind; I just didn't want to have to swim.

"This is the point of no return," says Henry as he sets up the first abseil. "After this there is no turning back. Ready?"

The gorge walls had suddenly closed in tightly. It was darker here and colder, designed to be intimidating. A snake swam away into the undergrowth as I looked over the first of the many waterfalls we would encounter. A week of bad weather had made the river higher than usual, adding to both the beauty of the canyon and to its challenge. The waterfall squeezed into the canyon with menacing force. This is what Henry had meant by "no escape plan"; once we entered the gorge we were committed to finishing it. There was no way to climb back up. Wondering if I should be committed myself, I watched Henry disappear expertly down the cliff face.

Then, suddenly, it was my turn. I clipped into the ropes and lowered myself gingerly over the edge; the waterfall's force was an unwelcome surprise, as it threatened to sweep my legs from under me as I tried to find footholds on the slippery rocks. I walked down the cliff carefully, placing my feet blindly beneath the white water that splashed into my face, its cold and brutal battering taking my breath away. Soon, though, I was at the bottom looking up at what I'd just done. I knew that despite some trepidation, I was going to have a really good day.

As a non-swimmer, I was most afraid of my head going underwater. Nevertheless, several abseils later I was sitting on the rocks above a slide, trying to work up the courage to launch myself into the deep pool of water that moments earlier had completely swallowed Henry, and where he now floated grinning and urging me on.

Keeping my knees bent and feet together, as instructed, I inched forward until the slippery rocks could take away some of my indecision. Suddenly the world was wet and claustrophobic and full of distorted shapes and colours. I was underwater and terrified, shocked into attempting to take deep breaths that proved impossible while the river boiled in my ears.

Thankfully, it didn't last long. The buoyancy aid I wore brought me bouncing to the surface. Although it made me feel a little overdressed (for most people, a wetsuit is enough), I was glad I had it. In fact, as I paddled for the edges of the pool I found myself so buoyant that it was hard to get my feet back on to the ground: Henry had to help me to stand up.

That was the good thing about doing this river with Henry. He knew it was difficult for me, he knew I was scared when I couldn't feel the riverbed beneath my feet or reach the sides of the pools, and he was always there to help if I needed him. Yet I never felt that I was following this river in any other way than off my own bat. I was not "being shown" the canyon, I was descending it as part of a team. As we had lunch after a long, technical abseil, I realised that Henry had possibly the best job in the world. "Not bad is it?" he said, looking at the primordial beauty around us.

A couple more abseils (and a few more slides that Henry had forgotten to tell me about, probably on purpose) and we reached the bottom of the canyon in an area called "the jungle". The canyon floor grew broader here, letting in sunlight to feed the African vegetation that characterises the Costa Tropical. Crawling through the undergrowth, we eventually found a path back up the hill. At the car, four hours after first squeezing into my wetsuit, I peeled it off with difficulty.

After sorting the gear we drove back to Almunecar. I was exhausted, the warm evening and the physical and mental effort of the day making it difficult to stay awake. Luckily I could just sit back and enjoy the view. The mountains were heavy in the sunset, and the Mediterranean far below was flat and still. Above the coastal hills the sky hung warmly, promising another glorious day of adventure to follow.

Canyoning trips are offered by a number of companies. Zate Aventuras in Almunecar (00 34 95 812 1472) offers day-trips for €75 (£52). Exploramas (00 34 95 259 9000 www.exploramas.com) in Mijas has a half-day trip in the Sierra Blanca for €40 (£28)