Northern Laos with its mix of stunning scenery and cultural sights is probably the most popular part for tourists. The three highlights in Laos and on most itineraries are the beautiful town Luang Prabang with its Unesco Heritage Old Town; Vang Vieng surrounded by a beautiful scenery offering lots of outdoor activities including tubing, and the capital Vientiane. But there is more to see. There is the sleepy border town Huay Xai where the beautiful two day boat journey on the Mekong to Luang Prabang starts, with a stop in Pakbeng. The village of Luang Namtha is well known for the trekking and the chance for homestays in one of the minority villages. Nong Khiaw along the Nam Ou river is a great place to enjoy great scenery and to relax. And there is Muang Ngoi, an one hour boat journey from Nong Khiaw, probably one of the most peaceful places to visit.
One place I haven’t visited is Phonsaven, famous for the Plain of Jars. It is a good place to visit by anyone who is interested in cultural sites.
You could easily spend weeks in this area (and I have done it) and it is important not too rush here. Take your time and you will fully experience this area.