The dawn in the heart of Central Vietnam does not simply break; it exhales. Out of the deep, subterranean limestone caverns of Phong Nha-Ke Bang National Park, a cold, damp breath of prehistoric air rises to meet the humid canopy of the tropical rainforest.

Every region carries a distinct olfactory signature that you can only truly appreciate at the slow, open pace of a bicycle. In the northern backcountry, you ride through cool forests of ancient hardwoods and wild ferns, the air thick with a sweet, damp fragrance of moss and wild jasmine.