Kuang Si Falls, are one of the most popular things to do while you are staying in Luang Prabang, so just get your swim suit and just enjoy them.
There are food and tourist stalls outside the waterfalls, but you can buy in advance in Luang Prabang as well. It is worth putting a whole day or more aside for seeing this place because it is a great spot to relax and meet others. There are multiple pools at different levels, all of which are reportedly safe to bathe in, and are extremely picturesque.
This place opens at 8:00 hrs. and closes at 17:30 hrs. and the admission is 20,000 kip.
How to get to Luang Prabang Falls?
When arriving at the falls, you will see a large multi-stage waterfall, accessible by boat or truck hire, some 29 km south of Luang Prabang. You can rent a motorbike to transport yourself there. Parking your bike at the entrance costs 2000 Kip. Shared tuk-tuks to go there charge about 30 to 50,000 kip. The cheapest seems to be near slow boat pier, though you can get them for 40,000 kip near JoMa Bakery. You may have to wait until the tuk-tuk fills up. Tuk-tuks are legally only allowed to take six people, and there is a checkpoint at the falls, so some drivers may try to get a 7th person in the front seat. A private tuk-tuk will cost you around 150,000 kip after some haggling. Drivers will try to show you some documents that quote 200,000 kip or more. Ignore it and insist on your price. Try and go with 5 people and insist on 30,000 kip each. Drivers should wait for 3-4 hours for you at the waterfall gate area. Make sure your 150,000 kip includes transport there and back. Bargain, bargain, bargain. Just remember that there are dozens of tuk-tuks around, so you have the advantage. If on your own, propose 30,000 kip, and if you have the patience wait until he finds more people. A seat in a mini bus costs 40,000 kip, more if booked through travel agent. Becareful of leeches in the water, especially if you climb to the top of the top of the falls. There is a lot of leeches in the water.
If you need more info check WikiTravel