Although little more than a speck of a reserve at just 48 sq km, hilly Phu Pha Thoep National Park (also known as Mukdahan National Park) has some beautiful landscapes and is scattered with unusual mushroom-shaped rock formations. The park is 15km south of Mukdahan, off Rte 2034.
For accommodation, there's camping and a three-bedroom bungalow that can sleep six.