Tartarus was the pit. Every time a monster was imprisoned or reformed in Tartarus, the place, they were actually on his true primordial body. The pit was really the deity himself. It was once prophesied that as it would take nine days to fall from Ouranos to Gaia, it would take just as long to fall from Gaia to Tartarus.( Sky to Earth, Earth to Underworld).
Once upon a time after the titans were destroyed by the gods, Gaia was furious. She decided that the gods needed to be punished. She went to her brother(ewww!) and had many children. These were the gigantes. There were 17 of them. One for each of the gods, two for Dionysus, one for Hecate, and one for the three fates. They were destined to destroy the gods, but, like always, the gods triumphed. One of the giants didn't even fight. Damasen was the bane of Ares, god of war. Since Ares was the god of war and Damasen was the complete opposite of him, Damasen was a peaceful giant. Tartarus thought he was a disappointment so he locked Damasen up in the pit.
Tartarus doesn't have many other myths because he was kinda like a one time hit. He didn't do much fore the next couple of millennia, but if you count the Percy Jackson stories as modern day myths then Tartarus makes an appearance in the second series , Heroes of Olympus. Percy jumps/falls into the pit with his girlfriend Annabeth. They traverse the body of Tartarus, where sand is glass and the air is heavily sulphuric, and wind up meeting the primordial himself. While they don't fight him, Iapetus,a titan who Percy forced to lose his memory(see also: Bob), and Damasen fought off Tartarus while Percy and Annabeth made it through the doors of death and saved the world.
Book where the battle with Tartarus takes place.