My fire pit is one half of a rock crusher machine. Another cone would be fitted on a frame so it is spaced a given distance from this one, and rock is fed in between the cones, while another part of the machine bounces the cones against each other repeatedly. This breaks the rock to the desired size, which is dependent on how far apart the cones are.
The steel they are made of can only take so much of the hammering until the surface is eroded away and begins to peen over at the edges and break off. The rock quarries sell them for use as fire pits, like this one. The thick steel acts as a great heat sink, the warmth radiating for hours after the fire burns down. Nice on late spring or autumn evenings, or even better for a winter bonfire.
A 15 image panorama, shot with a Pentax K-i, and Pentax-A* 600mm f5.6. Stitched and processed with Adobe Photoshop.