One of the most interesting things I've done was a trip to Bolivia and Peru a few years ago. We saw a lot of cool things (including a jaguar lounging beside a river as we took a boat trip), but one that really sticks in my mind was a hike I took with a friend one evening in the rain forest. The trail goes to one of the largest trees in the area, which looks like this.
It's a bit hard to get perspective from the photo, but this tree is about 7 feet in diameter above the buttresses, and probably approaching 200 feet tall. On the trip out, we had heard a big herd of white-lipped peccaries foraging near the trail. They have been known to (very rarely) attack and kill people, so we were joking about who would be the first up a tree if they charged us. We hiked to the tree, doing some sampling along the way, and then turned around. As we returned, it was getting dark when we passed the same spot, and the rainforest when it gets dark is a pretty intense place. We could hear the peccaries still grunting and clacking their teeth, and then there was a rustle right beside the path and we both froze. I was looking for a tree to climb, when a huge dark shape moved onto the trail. Still frozen, we watched as a tapir drifted across the path 20 feet in front of us, almost silent despite its bulk. The spell broke as it disappeared into the undergrowth on the other side of the path and we gave each other high fives, but the few seconds it was in front of us felt almost primeval, like stumbling across a dinosaur.
