Stonehenge in a Rock biome.
Stonehenge in a Greens biome.
Stonehenge is a randomly generated structure that spawns within the Greens or Rock biome on the Surface. It is made entirely of Stone. It has no chest, nor does it spawn any mobs different than would already spawn in the Greens. The only thing it provides is Stone and lore. It does also seem that if there is space below the stonehenge, the pillars will stretch farther down.