Phu Phrabaht Historical Park in Udonthani is an open-air museum with some unusual rock formations, scattered on a 3,430 rai plot of land.

Many of those have been made into religious shrines, and it is the setting for a local folktale called Nang Usa-Thao Barot, where Nang Usa, the female protagonist in the tale, was sent by her father to be educated in science by a hermit.

The  girl lived alone in this mushroom-shaped earthen pillar which thus became known as Ho Nang Usa, i.e. Nang Usa's Watchtower (fig.).