The Zrmanja River in Croatia is considered one of the most beautiful rivers in Europe. The best view is from the viewpoint of Pariževačka Glavica. Difficult to pronounce, but easy to find on Google Maps.
From here, you have a phenomenal view of the Zrmanja Canyon. A deep gorge through which the Zrmanja flows. Due to the bumpy road to get there, your rental car better be well insured.
This is also the most popular spot in the Zadar region for kayaking and rafting, but also one of the most beautiful places to swim. Definitely don't miss it if you're in the area!