This may be possibly one of the most beautiful places I have ever seen. Set in the mountains situated between Zadar and Zagreb is Plitvicka Jezera. It is a series of stunning turqouise freshwater lakes and waterfalls. The park is a world heritage site. You walk along the boardwork through stunning scenery but sadly are not allowed to swim. It can be pretty busy with the tourists but it really is a must see.
One of the most original sights in Croatia, the Sea Organ is a system of pipes and whistles set inside stone stairs that sigh and wail as the sea pushes air through them. It sounds especially magical when a boat passes by or even in a storm.