Plitvice Lakes is a staircase of sixteen lakes in the forested hills of central Croatia, each one a different shade of turquoise, each held back by a natural dam over which the water spills into the next, and you cross the whole thing on wooden boardwalks laid a few inches above the falls. The dams are the strange part. They are not rock laid down by the river but the work of moss and algae, which trap lime from the water and slowly turn themselves to stone; the barriers are still growing, so the lakes are still rearranging themselves. The water is clear to the bottom. Lean over a railing where it pools calm above a dam and you see brown trout holding in the current and old tree trunks lying whole on the pale floor, stiffened by the same lime. The colour shifts through the day and the seasons, from grey-green to a blue that looks dyed, depending on the light and on how much lime the water carries.
The lakes fall through a canyon in two groups. The upper lakes are wide and wooded, linked by dozens of small cascades; the lower lakes are pressed between limestone cliffs, and the boardwalks there run straight across the water with waterfalls on both sides. The canyon ends at Veliki Slap, at 78 metres the tallest waterfall in Croatia, and a platform at its foot puts you in the spray. Between the two groups lies Kozjak, the largest lake, crossed by an electric boat so quiet that you hear the beech forest on the shore. In April, when snowmelt drives the water to more than three times its late-summer flow, every barrier runs full and the falls are at their loudest; in October the beech and hornbeam turn copper and gold and the colour doubles in the still lakes below. Plitvice was Croatia's first national park, and the boardwalk is the same idea it always was: a way of walking on water that is busy building itself.