The best way to experience Krka is to have whole day excursion from Vodice or Sibenik with the boat.
Team and boat Lirica from Vodice are great! They go from Vodice at 9 am and come to Krka around 11. On the way to Krka boat pass Unesco city of Sibenik.
Think their web site is www.lirica-tours.hr
There is a free boat going to and from Skradin once an hour.
The boat leaves from Skradin at XX:00 and from Skradinski Buk at XX:30.
When getting of the boat just follow the crowd and you will reach the entrance to the park.
There are two options to get National Park of Krka, first one by the road from the town of Sibenik. The distance is about 10 km from Sibenik. You cannot drive-in by the car in the area of NP, only the official NP buses.
The second option is to get the small town of Skradin and then by the boat to the National Park. This second option is much more attractive, because you are passing by Roski Slap, one of the mine attractions in the park.
You will come to Skradin with local bus or your own vehicle. From Skradin take a boat, departuring every full hour. It'll take you upward Krka river, the scenery is beautiful with all the birds hiding in reeds and the cricket singing realizes you're still in Mediteranean area. You will arrive to Skradinski Buk after half hour.
The entrance ticket together with boat transportation will cost you 50 HRK (about 7 EUR).
The last ship from Skradinski Buk back to Skradin is at 7.30 PM.
Getting to/from Krka can be a challenge, but it also can be fun. From anywhere in Croatia, catch the train or bus into Sibenik. From Sibenik, get to the bus station and buy a ticket to Skradin. Once there, you will be able to jump on a ferry that will take you down a river and into the entrance to Krka. Getting away is the same, except you may be stuck for hours waiting for a bus back into Sibenik. If this happens, it's ok to hitch a ride with a local, I did, and it was free.
From Sibenik towards Skadrin (about xx km). From Skadrin with boat to first of many falls (Skadrinski buk)