One of the lesser-known features of the Machu Picchu archaeological site, the Inca Bridge is a “secret” entrance to the citadel. Built into a spectacular path along a sheer mountain side, the simple plank bridge could quickly be removed to scupper the progress of any unwanted arrivals.

The Inca Bridge (sometimes written as Inka Bridge) is a 25- to 30-minute walk from the center of Machu Picchu along a narrow path with some sheer drops down into the abyssal canyons below. And while plenty of tourists hike up Huayna Picchu, Machu Picchu Mountain, and to the Sun Gate, not many seem to go—or even know about—this alternative side trek.

The bridge itself, at least as it appears today, is a simple plank of wood that spans a 20-foot gap in the stone path. With the plank in place, Inca messengers could continue along the mountainside. But with the plank raised, would-be attackers or infiltrators would have a terrible time trying to cross the gap, especially with armed defenders on the other side. A unit of enemy soldiers would be sitting ducks, perilously exposed to arrows, slings, and hurled rocks.

For safety reasons, the Inca Bridge is blocked off to the public by a small gatehouse, but you can get plenty of good views of the bridge from the path. You can also see the extent of the incredible trail as it snakes away on the other side of the bridge, along an almost vertical mountainside. The path on the other side of the bridge is crumbling away in some sections, partly because any restoration efforts would be costly and dangerous.