Purple Worm

Purple worms are a subterranean monstrosity feared by all of those who travel in the Underdark. These massive creatures, known for devouring almost anything whole that they encounter, including rock and stone. As a result, they often connect different areas of the Underdark by burrowing through them, leaving perfectly cylindrical tunnels behind them.
According to some cultures, purple worms are the spawn of the Worm that Gnaws the World, Uluthog.