North Wales continues to develop as a leading adventure-activity destination, with the opening of the world’s largest fully underground zipline course.

In the vast Llechwedd Slate Caverns, Zip World’s latest attraction is a 10-line course that takes visitors on an aerial adventure through five caverns, some big enough to fit 75 double-decker buses.

The ziplines are interspersed with rope bridges, balance beams, tunnels and stretches of via ferrata: a mountaineering aid in which a harness is clipped to a cable running along a precipice.

Suitable for children as young as 10, the experience lasts around three hours. The walls of the cavern are illuminated by LEDs, transforming the dark cave into a vibrant environment.

The course was built over a period of 12 months, with workers swinging 100ft from the ground using an intricate network of wires and pulleys. Bottles were used for toilet breaks to “increases efficiency”.

Explorer and rock climber Eric Jones, 78, was the first person to experience the attraction. “It’s a perfect way for people from all walks of life to experience the thrill of adventure, in a safe environment,” he said.

The zipline course is the latest in a series of similar attractions to open in north Wales. Bounce Below, which opened last summer and is run by the same company, is a subterranean trampoline world suspended in a different section of the same slate caverns.

Above ground at the same site, Zip World Titan gives visitors the chance to fly down a line at 70mph, while another company, Zip Below Xtreme, offers a 130m underground zipline experience.

Ken Skates, the Welsh assembly’s deputy minister for culture, sport and tourism, said: “This collection of projects in north Wales is an excellent example of regenerating communities … they also show how we can work with our amazing Welsh landscape and heritage to create unique experiences and adventures.”