Sixteen blue and green lakes, stacked one underneath another, are linked by foaming cascades and pounding waterfalls at Plitvice, a Unesco World Heritage site in the Istria region of Croatia. Visitors can get a close-up view from boardwalks that carry them across marshes and along the lakeshores. The lakes flow into each other through a deep valley, with forested hills on all sides. As I walked along one of the hills, I could see one of the lakes emptying into another at the very spot where a boardwalk provided a classic “s” curve from one corner to another. All I needed to do was to wait for a few people to walk through my curve, and this pair soon obliged. From this high vantage point, the unique character of Plitvice becomes evident -- an ever-changing fluid landscape, created by water, gravity, limestone, and time.