My absolute favorite thing we did in Croatia was visit Krka National Park. Between hiking, boating, and swimming, this ended up being an incredible day. We opted to go to Krka over Plitvice because we were driving from Split and it was a few hours closer. We wanted to be the first people in the park.
We had heard that Krka and Plitvice were comprable, but Plitvice is just bigger. Krka ended up being pretty big as well, and is a great option if you just have one day. The one thing to know here:
Be the first ones in the park!
By the time we were finishing up our hike, hordes of people started pouring in. If we had been part of the large group, we probably would not have enjoyed our hike.
We also opted to take the boat to Visovac Monastery which was stunning. The boat ride there was awesome and the monastery was incredible in its beauty and serenity.
How to Krka:
There are a few options for entering Krka. We drove to Lozovac and took the bus down to the park. We then got ahead of the crowds and did the Skradinski Buk hike which can be done in a little over an hour if you push it. We had two hours to enjoy the hike, go for a swim, and get back to the pickup point for the boat to the monastery. If we had had more time, we could have driven to Skradin to park and taken the boat in. But this would have kept us from being the first in the park - so it ended up being a good decision to drive right in.