The city of Nakhon Phanom sits right ont he bank of the Mekong River, more or less directly across from the city of Tha Kaek in Laos. There isn't a lot to see in the town. Most people just pass through on their way to neighboring cities or to cross the river into Laos. But there is probably enough of interest to warrant spending a night here. See the Nakhon Phanom city map for an idea of what there is to see and where they are.
The thick forest of Wat Aranyikawat
The name Nakhon Phanom literally means 'city of mountains' but the modern city is completely flat. The mountains are across the river in Laos, in the form of jagged peaks that can be quite a dramatic sight in the afternoon. The name was given to the city by King Rama I in the eighteenth century.
The main spire (Phrathat Nakhon) of Wat Mahathat
The city was once part of the Lao kingdom of Lan Xang. One legend has it that a plague struck That Phanom in the seventh century or so, and the survivors settled first across the river in present-day Tha Kaek, and later moved back to the west bank, establishing what became Nakhon Phanom. However, this story is somewhat at odds with the history of the city's most important historical site: the Phrathat Nakhon spire, which was reportedly built in the year 607.
Governor's Mansion Museum
Tours of Nakhon Phanom city would mostly stick to the riverfront, which has a wide promenade on the banks of the Mekong, while the other side of the road is lined with several temples and other historic places. Starting at Wat Phra In Plaeng at the southern end of the esplanade, you can work your way to Wat Mahathat, the Indochine market, Wat Okat, the old Governor's Mansion, and end up at Saint Anna Church.
There are only a few hotels in Nakhon Phanom, and they are mostly tourist class places, but they will do for a night or two. Likewise, there aren't many restaurants in town, especially ones that have English speaking staff.