Rock climber Alex Honnold made headlines in June when he climbed 3,000 feet to the top of Yosemite’s El Capitan without a rope. But long before he stepped onto those granite cliffs, Honnold, like many of today’s leading climbers, first learned his sport in an indoor climbing gym.

Once regarded as an extreme sport, climbing has exploded in popularity in recent decades, thanks in part to the 400 such gyms across the U.S.

Even for people who would — quite wisely — steer clear of the kind of adventure Honnold pursues, rock climbing provides a bonanza of benefits from physical fitness to mental training to camaraderie.

And indoor climbing offers those benefits year-round, with air-conditioning, cushioned floors and everything climbers need to have fun and stay safe — including ropes.

Arizona’s first climbing gym, Phoenix Rock Gym in Tempe, will celebrate its 25th anniversary in August, and the Valley has gained several other gyms in recent years. They feature climbing lessons for adults as well as recreational clubs, competitive teams and summer camps for children. Many offer yoga classes and even Ninja Warrior-style fitness training. They rent climbing shoes and harnesses; host competitions; and provide a fun option for birthday parties and corporate team-building.

Although each gym is unique, they share some basic qualities. All feature rugged walls supported by steel framing and faced with either wood or fiberglass, which is coated with a textured paint to provide grip. The walls are shaped with angles, curves and overhangs that simulate natural rock features, but the color-coded climbing routes are created with plastic holds.

All of the gyms feature beginner walls with…