Gelatinous cube

A transparent oozes composed of mindless, gelatinous matter in the shape of a cube or rhombohedron, 10-15 ft. on a side and weighing as much as 50,000 lbs. They silently roam ancient crypts and vaults in regular, predictable patterns. As they travel the halls, they absorb any material in their paths from the floors and walls, including living creatures. Often they can only be detected by the undissolvable materials, like steel weapons, floating within their mass.