The Megalithic sites of Xieng Khouang province, better known as the Plain of Jars, are so numerous and shaped, unlike anything that you will see elsewhere in the world. Getting there is still pretty adventurous - it is either a flight or a bus ride from Vientiane / Luang Prabang. I did the latter (from Vientiane) and it took 13 hours.
Sites 1, 2 and 3 are the main sites to visit. Others have opened up now too, but they are not on the itinerary of the guided tours. I went on a minibus tour with 3 others, organized via a guesthouse in Phonsavan. The most interesting new development is the discovery of a quarry some km away, where they also found half-finished jars. Our guide told us that a foreign archeologist was working at the sites now, to piece together more about the history of the jars, who made them, and why. They will not apply for WH status until more scientific evidence is found to sustain the theory that the sites are cemeteries.
The visiting experience of the sites is still much as described below by the 2 reviews from 1997 and 2006:
You have to stay within the marked paths for fear of UXO's
The whole surrounding landscape is dotted with bomb craters and trenches
The road to sites 2 and 3 are still unpaved and bumpy
And yes, at least at sites 2 and 3 you are still allowed to climb on or in a jar to have your picture taken
There's an entrance fee now at each site (10.000 kip, 0,90 EUR), and at site no. 1 there's a little souvenir shop. All sites also have a small drinks&food stall. It is all very low-key. At sites 2 and 3 there were maybe 10 tourists when we were visiting, while there were about 30 (mainly Laotians) at the much bigger site 1 which is also the closest to Phonsavan. We went first to site number 3, and that is also the one I liked best due to its fine, idyllic location. Site 1 not only has the only jar with a carving on it, but also the biggest jar (2.5 meters) and the only jar which still is covered by its lid. The mysteries that still surround this Plain of Jars, the strangeness of the objects, and the remote location reminded me of Easter Island.