Lovecraft describes a Shoggoth thus:
"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."
He also mentions that, when spherical (e.g. in water) they are about 15 feet in diameter.
So does anyone make a decent Shoggoth that comes even close to this size?