Phra That Phanom is a tall spire - a style of pagoda (chedi) common to Northeastern Thailand and Laos. The tower sits inside a large temple formally called Wat Phra That Phanom Woramahawiharn. The tower is thought to have been constructed some time in the eighth to tenth centuries, but like many temples it has been renovated many times since it was first built. The last major reconstruction happened after the spire was blown over by high winds in 1975.
The tower is perhaps the most important of several thats spread around the northeast of Thailand. Phra That Phanom sits in the smallest of three concentric courtyards. The outermost courtyard is enclosed by a high wall that forms the outer wall of the sacred precinct, and encloses not only the tower, but the temple's main prayer hall and a large platform directly to the east f the tower where most people come to make offerings. The inside of the outer wall is covered and lined with Buddha images in a variety of poses.
The middle wall just encloses the tower, with a large area on the east side where people come to pray and make offerings. The inside of this middle wall contains several rather contemporary morality scenes with admonitions against drugs, etc. The innermost wall is just big enough to surround the base of the tower, and the doors in its four gates are rarely open. The spire has a large teak door on its eastern side, but I haven't found any information about what is inside.
West of the main enclosure are a few other buildings and structures of interest. Near the northwest corner of the outer wall is a large elaborate bell tower. Whether it is new, or simply newly renovated when I visited, I'm not sure. A little further to the west, descending from the platform that supports the religious structures, there's a small museum. I can't say it's very interesting, although just outside of the entrance a large section of the old collapsed tower is on display. Thought to date from the seventeenth century, when a monk from Vientiane came to rebuild the that, the cap-piece is cast from a number of different metals.
East of the main temple area is a large squat building that sits in a large pond. The structure is labeled Stupit That Phanom in large Thai letters, but there's no other information about what it is. There are two bridges across the pond to it, but the gates on both were closed and locked.
The temple is the center of an annual festival which starts on the 10th day of the third lunar month and runs for a week. The estimated date for the next festival is 5 March 2024. Note that hotels and guest-houses in the entire province are full up during this time, so if you expect to visit during the festival you'll need to book early.