The Great Pit of Carkoon was located within the Northern Dune Sea[1] on the planet Tatooine. The large depression in the sand was the home of a rapacious, if slow-eating, adult sarlacc on Tatooine.
Its proximity to Jabba's Palace, paired with the torturous death provided by the sarlacc, made it an ideal spot for executions to be carried out for Jabba the Hutt's pleasure.
Luke Skywalker looks down into the maw of the sarlacc.
The pit served as a site of execution for Jabba for many years, although it is unknown for how long the Sarlaac has been in residence there, although it was most likely present for thousands of years. After the capture of Luke, Han, Leia, and Chewbacca, Jabba took his rebel prisoners to the pit, to be digested over years by the sarlacc. The prisoners, Luke Skywalker, Princess Leia, and Chewbacca who the rebels were attempting to rescueHan Solo, managed to overcome their guards, with the help of R2-D2 and Lando Calrissian . While Luke, Han, Lando and Chewbacca fought on their Skiff and managed to knock Boba Fett into the pit, Leia used the chains she was bound in to strangle Jabba. Luke subsequently destroyed Jabba's sail barge and escaped with the rebels and the two droids R2-D2 and C-3PO.
The sarlacc went through a series of changes when George Lucas re-released the original trilogy as the special edition on VHS in 1997. Several additional tentacles and an extension with a beak-like tongue were added.
Note that while the original Star Wars Episode VI: Return of the Jedi showed Boba Fett falling in the pit and then lost from view, leaving some freedom to Expanded Universe authors to retcon his escape, the Special Edition CGI beak-maw actually is shown to swallow Fett. However, this makes little difference, as the beak-tongue's insides are the same as those of the pit in general.
"The Sarlacc is a soup, and the ingredients are all the people she's taken, over the centuries, over the millennia. Susejo's never admitted it, but I suspect that's all he is; the oldest of the soup's ingredients."