The monolith, which was over three feet [3 m] high and made of steel, was discovered by conservationists in the desert in the US state of Utah.
But just a few days after the discovery, the monolith had disappeared without a trace.
According to local authorities, the object must have been removed by an "unknown party".
The theories surrounding the monolith are many.
Several people on social media believe that the object should be an art project.
There are also conspiracy theorists who claim that it must have come from another planet.
According to local authorities, the monolith must have disappeared from its place on November 27.