You step off the air-conditioned van at a dirt lot where the jungle begins like a living wall—humid air, the smell of wet earth, and a chorus of unseen insects. Guides clip harnesses and hand you a helmet. Within the first hour your boots are streaked with red clay from an ATV track that cuts through secondary rainforest; by midday you are floating on a rubber tube into a shadowed cave, the river daring you to follow its black current; later you launch into the canopy, the wind flattening the day into a single sharp moment as the zipline pulls you over green roofs of leaves.