Loei is a sparsely populated, mountainous province in northeast Thailand, bordering Laos across the Mekong River. South of the laid-back capital, Loei, is the biodiverse Phu Kradueng National Park. Trails pass waterfalls and sandstone cliffs on their way up the huge plateau of Phu Kradueng mountain. North of the park are the striking eroded limestone formations of Suan Hin Pha Ngam, or “Beautiful Rock Garden.”
Area: 11,425 km²
Population: 634,500    Some  info with good information.
Dan Sai Folk Museum –The region’s famous festival is called Phi Ta Khon, or Ghost Festival and celebrates a time in ancient history when Prince Vessantara (Buddha in his final life) left for a journey and his followers presumed he was dead. His return was a surprise which caused wild and loud celebrations which were said to wake the dead. The date varies each year (somewhere between March and July) and is selected by the mediums in the Dan Sai district. During the three-day festival, participants wear colorful masks made from rice husks and rice steamers along with colorful patchwork clothing which at the end of the festival, they shed and let drift away in the river.
Phu Ruea National Park – I was off the charts excited when I learned I’d be visiting this park because, well, because it’s a national park. It’s also the coldest spot in Thailand during the winter season. The park is about 46 square miles with a pine forest, winter flowers, waterfalls and caves. Unfortunately during my visit, it was an extremely foggy day at Phu Ruea National Park and I didn’t get to see much, but, what I did see was still breathtakingly beautiful.  great info you can find here.  http://solotravelgirl.com/hidden-thailand-10-things-to-do-in-loei-province/
If you visit North Thailand Fly to UdonThani International Air port and stay with Us will show you about Udon Thani and Nongkhai.