The menhirs are tall, living, rectangular-prism-shaped stones native to the Plain of Fear. They appear to grow with time but are rarely seen in motion. They are the creations of Old Father Tree, a god that created the entire Plain of Fear with his dreams. They are not animated by magic, as noted by Croaker, because they function without impediment inside the "null" surrounding Darling. A 12-foot-tall menhir is considered by humans to be a "runt".
They are intelligent beings that are often used as a medium for communication between Old Father Tree and humans on the Plain. When the soldiers loyal to Darling shelter in the Plain of Fear, the menhirs often warn them of dangers and help maintain the strong alliance. They do not often provide complex or complete information despite being capable of doing so.
When a menhir falls on its side, it loses its intelligence and mobility, and will be found upright and silent shortly after.