The Pearl of the Andes by Gustave Aimard

Curumilla and his two companions descended the steep sides of the Corcovado; if the ascent had been difficult, the descent was not less so. Everywhere escaped thousands of hideous creatures; and not unfrequently they caught glimpses of snakes, unfolding their threatening rings under the dead leaves which on all sides covered the ground. Sometimes they were obliged to crawl on their knees, at others to jump from branch to branch.

This painful and fatiguing march lasted nearly three hours. At the end of that time they found themselves again at the entrance of the grotto where they had left their horses. The two white men were literally knocked up, particularly the count. As for Curumilla, he was as fresh and active as if he had not gone a step. Physical fatigue seems to have no hold on the iron organisation of the Indians.