Sam K
Google
This is a beautiful temple complex that predates Angkor Wat.
You need 1-3 hours, depending on how much time you want to spend going in and out of the buildings in the main complex, whether you want to hike up to see the crocodile rock, the elephant rock and Buddha's footprint.
It's 55k kip/person to enter (currently about $2.50 usd), and there's an electric shuttle that takes you from the ticketing area to the temple complex.
I'm very glad that we decided to come to southern Laos and see this complex. Definitely a great addition to our trip.