The centre opened two-and-a-half years ago and now serves more than 20,000 climbing enthusiasts. The interior boasts an expanse of highly realistic crags (artificial rock faces or boulders) that vary in height and shape. There's a strong social atmosphere at the centre where dozens of people, quite literally, hang around. Some climb upside down "bouldering" while others are suspended in mid air or cling precariously to small foot- and hand-holds high above the ground.
"When you come here you're setting your own problems and achieving your own goals," says Michael Lamb from the Castle Centre.
"We have all kinds of people here, from road sweepers to city gents earning pounds 100,000 a year," he continues. "There's a strong community feel and different groups often get together and hire a bus for a climbing trip."
The mechanics of the sport appear simple enough. Your legs are three times stronger than your arms, so climbers constantly try to shift body weight onto them. Hands can only support 20 per cent of body weight, so the legs are used - even when participants are hanging upside down.
Climbing is not reliant on physical strength. Success is 90 per cent mental and 10 per cent physical as climbers have to plan the route up the rock face. In this respect, the sport provides a challenge for prospective climbers of any physical ability.
"Indoor climbing is a sport in its own right; many people don't want to go outside," says Lamb. "If you don't fancy a trip to the gym, you come here instead. It's a great feeling of achievement when you reach the top of a wall."
Different specialities require different techniques; bouldering doesn't require ropes, just the ability to climb upside down like a spider over bulbous rocks
Top rope climbing involves working with a partner. The climber is attached to a rope while his/her partner stands below "belaying". This involves turning "live" rope into "dead" rope - drawing in slack rope as the climber ascends the crag.
More experienced climbers work without top ropes and clip their harnesses to secure points (metal bolts attached to the rock) as they pass. When you fall off the crag you're locked onto the wall.
Twenty-seven-year-old Adrian has been climbing for three weeks and seems converted by the experience. "The first time I came, I was in awe of the place - there were people climbing the walls like spiders defying gravity.
"It's harder than it looks," he reveals, "but I recommend it to anyone. I've tried other sports but climbing is so progressive, everyone has their own style and you can always get better."
Bob Hegram is at the centre with his 10-year-old son Sammy. "Climbing takes me away from the things I normally do," he says. "It's all about pitting yourself against something as an individual - which appeals to me."
Sammy is also hooked. "I play football, but I like climbing better. When you're bouldering there are no ropes, but it's OK to fall."
The Castle Climbing Centre, Green Lanes, Stoke Newington, London N4 2HA (0181-211 7000)
The centre offers four modules. "Getting Started" teaches beginner safety procedures, belaying and harness attachment.
"Developing Technique", "Climbing Higher" and "Lead Climbing" complete the set.
All you need is trainers, a tracksuit and a willingness to try something new. Equipment (including climbing shoes) is available to rent.
Prices for adults (after registration) start at pounds 6/pounds 3.50 concessions and pounds 3.50 for children