Over the centuries, control of the province swung between the Thai Kingdom Ayutthaya, and the Laotian kingdom Lan Xang, as their respective powers ebbed and flowed in the region.
The Prap Ho Monument in front of the historic city hall (now a museum and cultural center) memorializes the war dead of the Haw wars.
In more recent years, Nong Khai has become a popular destination during the Buddhist Lent festival when mysterious balls of light, or Naga fireballs, rise from the Mekong River. The balls resemble an orange sun. They rise out of the river approximately 6–9 meters (20 to 30 feet) and disappear after three to five seconds. Although the fireballs can be seen at other times, most Thais travel to see them during the full moon in October when the incidence of them is considered to be much higher.
Nong Khai's main sight is Sala Keoku (alternatively spelled as Sala Kaew Ku, also known as Wat Khaek), a park of colossal sculptures, some over 20 m tall. The park is the handiwork of the mystic Luang Pu Bunleua Sulilat, who bought the land in 1978 when he was exiled from his native Laos, where he had built a similar park in Vientiane in the 1950s. Synthesizing Buddhist and Hinduist ideologies, Buddhas, many-armed goddesses, a seven-headed Naga snake, and various human-animal hybrids dominate the site.