Wat Si Mongkhon or Wat Na Sai is located at Mu 3, Ban Na Sai, Wang Ban Sub-district on the Wang Ban Intersection – Cho Wo Route. It is an ancient temple of Phetchabun. The interesting point of this temple is its mural paintings inside the Ubosot, depicting the Jataka stories, the Heaven and Hell, and those reflecting the local lifestyles in the past such as occupations and junk trade.

To get there  Take the Lom Kao – Wang Ban Route for 3 kilometres from Lom Kao District. There will be a 1-kilometre path into Na Sai village.