Phra That Phu Phek is an ancient stone sanctuary of historical and astronomical significance, located on Phu Phan mountain. It was built during the ancient Khmer period around the 16th Buddhist century as a Hindu religious site, before later being converted into a Buddhist one.

The temple's structure is made of sandstone on a laterite base, with a square plan and indented corners. The front connects to a rectangular mandapa. The sanctuary itself is 7.67 meters high and was left unfinished, with no roof or spire; only the crossbeams were put in place.

According to the legend of Phra That Phanom, a group of men built Phra That Phu Phek to compete with a group of women who were building Phra That Narai Cheng Weng. The condition was that the first to finish would enshrine the Buddha's relics. However, the women played a trick by lighting a fire in the shape of the star "Phek" in the sky, causing the men to mistakenly believe it was morning and stop their construction. This is why Phra That Phu Phek was never completed as we see it today.

Phra That Phu Phek is also notable for its ancient wisdom, as the sanctuary's structure functions as an astronomical calendar. Studies have found that on significant seasonal days, such as the equinoxes (March 21 and September 21), sunlight shines through one of the square openings in the structure, demonstrating the incredible architectural and astronomical knowledge of the ancient people.

If you are a fan of historical and natural tourism, or if you want to witness the wonder of the ancient astronomical calendar, Phra That Phu Phek is a place not to be missed.

• By private car: From Sakon Nakhon city, take Highway 22 (Sakon Nakhon-Udon Thani) until kilometer 139. Then, turn left onto Rural Highway 2016 towards Ban Phu Phek and drive up the hill to the parking area.

• To reach the temple: You must walk up a stone staircase of approximately 491 steps from the parking area.

• The path to the temple is quite steep and involves many steps. It is recommended to be physically prepared, wear comfortable shoes, and bring drinking water.

• The best time to visit is in the early morning or late afternoon when the weather is not too hot, and you can enjoy the sunrise or sunset views.

• There is a viewpoint at the top where you can see a wide panorama of Sakon Nakhon province.