It was a terrible, indescribable thing vaster than any subway train—a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and un-forming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter.
— H. P. Lovecraft, At the Mountains of Madness
A shoggoth (occasionally shaggoth) is a monster in the Cthulhu Mythos. The being was mentioned in passing in sonnet XX ("Night-Gaunts") of H.P. Lovecraft's sonnet cycle Fungi from Yuggoth, written in 1929–30, and were expounded upon in his novella At the Mountains of Madness (1931).