UPPSALA, Sweden — About 100 yards inside one entrance of the Lunsen forest is a rock ledge formed millenniums ago when all of Scandinavia was covered by ice. A thicket of bushes lines the near edge of a gully that drops down 15 feet. On the far edge, a group of trees rises, like fingers splayed wide, providing the false impression that they are not so far away when in fact, a steep fall awaits anyone who steps off the precipice. To the side of the ledge is a medium-size stone.

“So look,” Thierry Gueorgiou said one afternoon, pausing just before the ledge and pointing to a folded map. “See that rock? It is this tiny, little black dot here. And so we must go down the other side.”

With that, Gueorgiou — a lanky Frenchman with a perpetual bounce — was off again, his sneakers crunching over branches. His voice rose in excitement as he explained that the key to his dominance in the sport known as orienteering was an innate ability to quickly convert a two-dimensional piece of paper with a variety of symbols on it into a three-dimensional route through the woods.

He passed a gap in the trees. “Crisscross,” he said, tapping the little symbol on his map. Then came an open field of tall grass. “Shaded light green,” he said. “And also orange, because it’s a clearing.”