This loop takes you from Udon, to the west, and the little town of Loei, then along the Mekong, the natural Thai-Laos border, through Nong Khai, and on to Nakhon Phanom. With a side trip to That Phanom (and a possible stop at Ban Chiang), you return to Udon, from where you can fly back to Bangkok. You could also amend the route to follow the Mekong all the way south from Nakhon Phanom to Ubon Ratchathani. This is adventurous off-the-track travel, and it's not a bad idea to hire a car and driver.
520km (323 miles) NE of Bangkok; 344km (214 miles) N of Nakhon Ratchasima
Cool and usually rainy because of its higher elevation (the town is reputedly the coldest spot in the kingdom), little Loei is a lazy riverside town worth an overnight stop, but this route is more about the beautiful road journey, not the destination. Dan Sai, 80km (50 miles) southwest of Loei, hosts the annual Pi Tha Khon Festival (June/July), a Thai-style Mardi Gras in which young men dress as spirits and go crazy in the streets. "The devil made me do it!" is the excuse for all kinds of outlandish behavior; it's lots of fun. South of Loei town is Phu Kradung National Park (admission 400B adults, 200B children), one of Thailand's most dramatic sights: a bell-shaped tabletop mountain of 1,300m (4,265ft.) that can be climbed in around 3 to 4 hours (porters can be hired to carry bags) and has appealing log-cabin huts (900B-3,600B double) for visitors to stay on the summit. The park is 82km (51 miles) from Loei and well worth the trip, especially in December and January when the scarlet maple leaves are falling, though it's closed during the rainy season (June-Sept).