Yuggoth... is a strange dark orb at the very rim of our solar system... There are mighty cities on Yuggoth—great tiers of terraced towers built of black stone... The sun shines there no brighter than a star, but the beings need no light. They have other subtler senses, and put no windows in their great houses and temples... The black rivers of pitch that flow under those mysterious cyclopean bridges—things built by some elder race extinct and forgotten before the beings came to Yuggoth from the ultimate voids—ought to be enough to make any man a Dante or Poe if he can keep sane long enough to tell what he has seen...
—H. P. Lovecraft, "The Whisperer in Darkness"
Yuggoth is the planet where the extraterrestrial Mi-go have established a colony. The Mi-go's city sits at the edge of a pit wherein dwells an ancient and horrifying entity feared by the Mi-Go. They periodically abandon the city on those occasions when it rises from the pit and can be seen directly.
The being Cxaxukluth, along with Tsathoggua and his parents, migrated to Yuggoth from Xoth. A dysfunctional family in their own right, Cxaxukluth's progenies abandoned their patriarch and sought refuge deep in the bowels of Yuggoth, owing to Cxaxukluth's cannibalistic tendencies. Soon thereafter they fled Yuggoth, though Cxaxukluth still dwells there to this day.
On Yuggoth, the Mi-go mine a strange metal known as tok'l. Tok'l-metal is used in the manufacture of the Mi-go's notorious "brain cylinders", but it also has other ritual uses as well.
Yuggoth itself hung directly overhead, obscenely bloated and oblate, its surface filling the heavens... and all the time pulsing, pulsing, pulsing like an atrocious heart, throbbing, throbbing.
—Richard A. Lupoff, "The Discovery of the Ghooric Zone—March 15, 2337"
In Richard A. Lupoff's short story "The Discovery of the Ghooric Zone—March 15, 2337", Yuggoth is hinted to be the hypothetical Planet X. Lupoff's Yuggoth is a colossal, crimson planet, twice as massive as Jupiter. It is flattened at the poles and pulses eerily, no doubt because of its tremendous rotational speed—perhaps as fast as 80,000 kilometers per hour. It has numerous moons, including Nithon and Zaman, and the twin-moons Thog and Thok.
Nithon is a cloud-laden moon of Yuggoth. It is covered by fungi and has luminescent clouds that block all sunlight.
Thog and Thok are twin moons of Yuggoth. Very little is known about these moons, though Thog is said to be a pitch-black world. On the surface of Thog is the fabled Ghooric Zone—a green-litten subterranean cavern containing a putrid lake where "puffed shoggoths splash".