Plitvice Lakes is a waterfall system that is still building itself, stone by stone. Its sixteen lakes sit in a staircase of natural dams made of travertine — a porous rock that forms as calcium carbonate settles over moss, algae and bacteria. Those dams are alive and grow a little every year, so the shape of the lakes shifts over centuries and the park's map is never quite finished. The water steps down about 133 metres from the highest lake to the lowest, spilling over hundreds of barriers before gathering into Veliki Slap, at 78 metres the tallest waterfall in Croatia. Twelve wooded upper lakes rest on soft dolomite, while four lower ones are cut into a limestone canyon. Croatia made this its first national park in 1949, and UNESCO listed it as World Heritage in 1979 for exactly this rare, living process of stone-building water.
Walk the wooden boardwalks that run just above the surface and the water is so clear you can pick out trout and whole fallen trunks on the bottom. Its colour is never fixed — azure, emerald, grey or deep blue depending on the minerals, the microscopic life in the water and the angle of the sun. An electric boat carries you silently across Kozjak, the largest lake, and in October the surrounding beech forest turns copper and burns in the reflections. Brown bears, wolves and lynx live in the forest beyond the trails, though they are almost never seen. It came close to being lost: the first fatal clash of the war for Croatian independence broke out here in 1991, and the park spent 1992 to 1997 on the List of World Heritage in Danger. Today it is fully recovered and the country's busiest natural attraction — so busy that entry is now capped by timed tickets, and swimming in the lakes is forbidden to protect the fragile travertine.