Inside the World’s Biggest Rock Climbing Wall Manufacturer Rock climbing used to be a sport for self-described dirtbags living out of their cars, traveling in search of the perfect crag. It’s now gone mass market, leading a new indoor climbing gym to open in the U.S. almost every week. Behind the boom is Walltopia, a Sofia (Bulgaria)-based company that grew from the rubble of communism’s fall in the 1990s and has since become the world’s largest manufacturer of artificial climbing walls. At the helm are two childhood friends who met climbing at their local crag: Ivaylo Penchev, a theoretical physicist-turned-serial entrepreneur, and Metin Musov, who oversees the company’s 250-worker factory in Letnitsa, a rural village of 2,547 people. Photographer: Guy Martin for Bloomberg Businessweek By Esmé E Deprez @esmedeprez More stories by Esmé E Deprez November 10, 2015, 9:00 AM EST Walltopia’s Ivaylo Penchev climbs at Boulderland, Walltopia’s gym in Sofia, Bulgaria. Workers sprinkle quartz sand at Walltopia’s factory in the rural town of Letnitsa. Painting wall panels. A welder at work on the steel frame for a wall. Workers fabricate a wall feature. A Walltopia employee holds a just-sanded climbing wall boulder. It’s made out of treated and heated wood so it can become an obstacle on one of the wall systems. At the Letnitsa factory, a worker paints a steel skeleton. A mold is injected with resin to make a climbing hold. A customer at the Walltopia gym in Sofia climbs during the late afternoon.