It's a gas fire pit. The pit is formed by using a concrete pipe section, or collar, that is made for constructing man holes. The pit has a cover which we had made by slightly modifying a cast iron tree grate. There is a frame for grate which has been attached to the top of the concrete section.
There is a circular fire spreader attachment on the end of the gas line about 1 foot down, this makes for a wider, more attractive, fire. The fire spreader is buried in fire cinder. Don't use rock to cover the gas element, they can explode. Good luck. Scott