Why visit one lake when you can visit 16? Croatia's Plitvice Lakes National Park, one of the largest and oldest in the country, provides that exact opportunity thanks to a unique geological feature. The slopes of the Mala Kapela, Medveđak and Plješevica mountains funnel water into the Plitvice plateau. This water carries precipitated limestone, which gradually accumulates and hardens over time, creating a series of rock barriers called tufa. These barriers form pools, with thin, lacy waterfalls leading from one 'lake' to another. This majestic display of geology and hydrology draws over a million visitors to the paths and boardwalks that wind through the lakes—they are a UNESCO World Heritage Site, after all. Even in the winter, the lakes retain their beauty, with once-roaring waterfalls frozen in place.