Croatia: Plitvice Lakes National Park
This is an absolute natural wonder of the world (and UNESCO recognized it, it was one if the first awarded this as a natural site) and so far the top attraction I have seen in Croatia. It is the largest national park in the country and is a series of waterfalls and lakes as the river carves its way through a limestone karst landscape. There are 16 lakes total, all interconnected by the flowing river, all on different elevation levels, with crystal clear water. It’s like a site from Avatar!