Climbing is a circumscribed sport. Firstly by geography, as all city-dwelling climbers know: moving down to London after a summer's climbing in Northumberland, I soon found that far fewer of the landmarks are vertical, and of those, even fewer are scalable - unless you fancy having a crack at Nelson's Column and spending the night in a cell. The second problem climbers have to overcome is the weather. In winter, unless you are prepared to go to the expense and hassle of a trip abroad to find some real snow - or real sun - you're stuck indoors. English drizzle just doesn't cut it. So what is a climber, living in London in winter, to do?
In order to find out, I enlist the help of Tom, a climbing acquaintance of mine. His pedigree is good: he spent New Year's Eve in the south of France doing things with crampons and ice axes, and soon he is going west to America for some more of the same. He has been climbing on rock and snow since an early age, and he's good at it.
Tom takes me to the Castle Climbing Centre in Stoke Newington, north-east London. From the outside it looks as if it has been lifted straight out of an Edgar Allen Poe novel: a mish-mash of high walls, turrets and crenellations perched darkly on a grassy rise, incongruous against the backdrop of traffic that surges past on the road below.
In fact, its history is far more prosaic than its appearance would suggest: it was originally a Victorian pumping station, and is now leased from Thames Water. Inside, the odd piece of heavy machinery lurking in the corners provides the only evidence of the building's industrial heritage. Other than that, everything is light, bright, garishly colourful and, taken together, resembles nothing more than an outsize adventure playground for grown-ups.
For those of you who haven't been to a climbing centre, imagine a series of walls speckled with multicoloured hand- and foot-holds, ranging in size from big, scoop-shaped handles to minute crimps that most of us wouldn't consider large enough to make effective toothpicks. The air smells, not unpleasantly, of chalk dust, rope and sweat.
Unlike outdoor climbing, which involves equipping yourself with a bewildering - and expensive - array of nuts, wires, camming devices and karabiners, climbing indoors requires only a pair of climbing shoes, a harness and a belay device (a form of brake clipped on to your harness which allows you to control the descent - or arrest the fall - of the person who's climbing). Most of the routes are top-roped (a rope is suspended above them from a point at the top of the wall), meaning you don't even need to bring your own rope.
We get our kit on and I tie the rope into my harness. Although reasonably well-acquainted with the techniques required to get me from the bottom of the wall to the top, I am slightly nervous about climbing with someone who is manifestly better than I am; however, I manage not to embarrass myself and make it to the ceiling without incident. Despite the comparative safety of climbing indoors - so long as you maintain your concentration - I still feel the adrenalin thrill brought on by climbing a potentially lethal distance above the ground. Which is, of course, exactly the thing that makes climbing so compelling.
When Tom tries a route, I perceive the difference between someone - like me - who scrambles up the wall using any and all available teeth, fingernails, elbows and knees, and someone who actually knows what they're doing. Contrary to the anoraks-and-beards image with which the sport has unfortunately been endowed, climbing can be an improbably elegant - almost balletic - activity. Tom's movements up the wall are unhurried and controlled. He makes it look easy, although I know from personal experience that it's not.
Between routes, I ask Tom about the climbing he's done before. His stories of 60ft falls and ice routes up waterfalls in America are more than a match for my tale of that time I got caught in the rain in the Lake District. I decide not to mention it. Given his intrepid history, what is the attraction of a cosy indoor centre in London?
"To be honest, it's mostly for the training, to keep fit," he replies. "But then the atmosphere's friendly and the people are nice, and it's always good to be climbing. And what else is there to do in winter?"
Good point. After wearing ourselves out, we head upstairs to the cafe for tea and chocolate muffins, which resemble small mountains in their size and density and so conform neatly with the day's climbing theme. The cafe is set in the middle of the first floor's higher walls. On a Wednesday afternoon the centre is pleasantly empty, but we still spend half an hour or so watching various pairs popping up and down the more strenuous routes. One couple in particular - an older man and a wiry-looking woman - dispatch in quick succession a number of routes that I wouldn't attempt without the aid of a crane and a winching device. Tom tells me he's seen them there before. "Some people get obsessive about it," he says, "but for me it's more about just getting out with your mates and having fun. I'd rather enjoy climbing a route that's well within my capabilities than struggle my way up something really tricky just to prove I can do it."
That said, one of the benefits of the controlled environment of the climbing wall is that you can climb to the edge of your ability without really placing yourself in any danger (one of the reasons why it's the ideal environment in which to introduce kids to the sport). In my case, this happens when Tom suggests I try leading a climb.
When you're following someone up a route a great deal of the danger is removed: the rope is taut above you, and if you fall, it will only be a matter of inches. If you are leading a climb, however, you have to clip your rope into pieces of protection as you move up: climb 6ft above your last piece of protection and you'll fall 12ft if you lose your footing - a much scarier proposition. At the Castle, though, there are plenty of easy routes where you can get a sense of how it feels to climb above your rope without being in any serious danger of taking a fall. Tom goes up first to show me the right way to clip into the karabiners hanging from the wall, and then it's my turn. While the climb itself is easy, there is something distinctly unnerving about the knowledge that any error will result in a lengthy drop. Half the effort is mental: trusting yourself to make the next move without falling off. By the time I get down my legs feel slightly wobbly but, addicted to my own adrenalin, I find that as soon as I am standing on the ground I am keen to have another go.
We warm down on a couple of easier routes, and soon Tom is making a series of internationally recognisable hand-to-mouth gestures in my direction. A climber ex-boyfriend of mine, when asked why he climbed, replied "Because the beer tastes sweeter", and certainly there's nothing like a bout of exercise to make you feel like you deserve a drink - or several - afterwards. We repair to the nearest public house, settle down with a couple of pints and begin to tell each other about climbing exploits past, present and - hopefully - future. There's one undeniable benefit of climbing in the city: instead of having to walk down a mountain, the pub is just across the road.
· Sarah Crown and Tom Palin went climbing courtesy of the Castle Climbing Centre, Green Lanes, Stoke Newington, London N4 2HA. Opening hours are Monday to Friday 2pm to 10pm, and Saturday and Sunday 10am to 7pm. The Castle runs four-week introductory courses for £99 including equipment hire. They also have leading and bouldering courses. Otherwise, entry costs £7.50 for registered members and £8 for guests. For more information, call 0208 211 7000, or visit their website at www.castle-climbing.co.uk.
Looking for a climbing wall near you? Most cities and towns now have at least one wall. Call the British Mountaineering Council on 0161 445 4747 for more details.
