Barro Colorado Island

Barro Colorado Island exists because of an accident of engineering, but what happened to it afterward was entirely deliberate. When the Chagres River was dammed in 1913 to form Gatun Lake, the rising water isolated a hilltop that became, overnight, an island — and in 1923 it was designated a biological reserve, making it one of the very first tropical forest sites in the world set aside specifically for continuous scientific study. The Smithsonian Tropical Research Institute has run it ever since, which means researchers have been observing this exact 1,500 hectares of forest for over a century, longer than almost anywhere comparable on earth.

Visiting requires a permit arranged well in advance through the Smithsonian, and access is limited to guided groups accompanied by trained naturalists rather than independent exploration — a restriction that initially frustrated me and that I came to fully respect within the first half hour on the trail. Our guide, a research assistant working on a long-term seed dispersal study, could point to individual marked trees and describe data collected on them going back decades, an intimacy with a single patch of forest that felt genuinely different from any other guided hike I’d taken.

The wildlife density here reflects a century without hunting or clearing — we watched a troop of white-faced capuchins move through the canopy in a tight, noisy group, and later, on the trail back to the dock, a coati crossed directly in front of us with total indifference, evidently as habituated to researchers as the researchers are to it. Agoutis, a rodent about the size of a large rabbit, moved through the undergrowth constantly, functioning as one of the forest’s key seed dispersers for the enormous trees whose fruit they bury and occasionally forget.

When to go: Visits run year-round but must be booked months ahead through the Smithsonian Tropical Research Institute, as group sizes and dates are strictly limited to protect the ongoing research.