Believe it or not, some people on earth haven't seen fireflies. Fireflies are a staple of summers in the American South, alongside the chirping static of cicadas. Congaree National Park's fireflies are extremely special. Every year, at some point between mid-May and late June, the Carolinian fireflies put on a spectacular, synchronized show. Now an annual tradition, the park itself has a Fireflies Trail and accompanying tour that can, understandably, get pretty busy. To see this amazing natural phenomenon, however, it's worth carving out a night just for this once-in-a-lifetime opportunity.