The X-Pit, or simply the Pit, was an Apokoliptian prison.
After the trade of infants by Darkseid and Highfather, Scott Free was trained and tortured in the X-Pit on Apokolips by Granny Goodness into becoming a loyal denizen of Apokolips. Scott tried to escape many times, and eventually succeeded, overcoming its innumerable traps and security devices.
Virman Vundabar eventually took control of the X-Pit and remodeled it into his own personal fortress, completely changing the interior and the traps. Vundabar held Kalibak prisoner in ther X-Pit during the civil war that ravaged the planet. Scott Free was recruited against his will by Granny, who held Oberon hostage, to liberate Kalibak. With help from Big Barda and Flash, he succeeded.
The X-Pit features in Mister Miracle #2, published in May–June 1971, written and drawn by Jack Kirby. In this version it is based on Earth not far from the country house where Mister Miracle lives. It consists of a deep well with a transparent cage at the bottom which releases various elements upon its prisoners including fire, rising mud and radiation. Granny Goodness traps Mister Miracle (aka Scott Free) and Oberon inside but they escape and destroy it and its creator, Overlord.