Nong Khai has one sight that cannot be missed - Sala Kaew Ku or Sala Keoku, also known as Wat Khaek, located 6km east of Nong Khai on Highway 212. It's on the side of the road going towards Nong Khai you'll need to make a U-Turn if coming from Nong Khai. Once you turn off the road, the site itself is about 1-1.5 km away on the left.
This utterly bizarre park of massive sculptures some over 20m tall is the handiwork of the mystic Luang Pu Bunleua Sulilat, who bought the land in 1978 when he was kicked out of his native Laos - a similar park of his earlier work remains near Vientiane. Synthesizing Buddhism and Hindu ideologies, Buddhas, many-armed goddesses, naga snakes and all sorts of human-animal hybrids dominate the scenery. Entry is 20 baht for Thais and Foreigners July/August 2011.
There is no direct public transport and you might find it a little tricky to get back, so you're best off arranging a return ride with a tuk-tuk 100 baht or so, including the cost of the driver waiting one hour or hire a motorbike at Limmaneemotor in Nong Khai. You can also contact Khao Niao Tours listed above for private tour in an air conditioned vehicle starting from 100฿ per person. As well they offer free maps explaining the individual statures of the Wheel of Life which is invaluable when walking around. Maps are in English and can be picked up from their local office.
Particularly noteworthy is the Wheel of Life, depicting his theory of the cycle of life; you enter via from a womb-shaped tunnel and walk the circle past statues depicting the stages.
Luang Pu's mummified remains are enshrined on the third floor of the Sala Kaew Ku pavilion itself.
