A Lazarus Pit has longevity, rejuvenation, and youth restoration properties. By bathing in a pit a person can have their wounds healed, the old are made young and the dead can be brought back to life. The pit can only return from the dead those that have just died, anyone who has been dead for a long time can not be resurrected again. For a time a pit could only be used once before its chemical properties become inert.
Submerging oneself into a pit will give them heightened strength as well as drive a person mad for a short time; they could attack anyone around them and must be avoided or restrained until they return to sanity. Anyone who uses the pit and is not injured or dying will be killed. The chemical properties of the pit can destroy the undead as well.
Ra's al Ghul discovered the Pits by accident when trying to save a prince's life. He put him into the pit, instantly healing him back to perfect health. A side effect however was that it made him clinically insane and as a result he killed Ra's wife. However Ra's was found guilty of her death and sent to the desert to die, but saved by a tribe and a boy named Huwe. For some time, he used the Pits along with Huwe and Ra's uncle. Huwe died much later, and his uncle went missing.
Batman and Bane went around the world in order to destroy all the Lazarus pits that existed. It was believed for a time that Ra's al Ghul possessed the last remaining pit in existence, however it turned out that there were still several that were hidden.
One belonged to Ra's al Ghuls long lost daughter, Nyssa, who discovered a way to use the pit indefinitely, where as before each pit could only be used once. There is a pit located in the Batcave, created in order to keep balance in the world. Another exists in the Himalayas, where Black Adam used it to return Isis back to life. One exits in the Australian outback, another is located in Tibet and still another is hidden in England.
Fountain of Essence
During the Resurrection of Ra's al Ghul, it appears that Ra's has discovered a pit that has all the benefits of the Lazarus Pits, but none of the side effects. It brought him back to life after being dead far longer than the Lazarus pits can resurrect someone, however it brought him back in a crumbling body. Both Sensei and a wounded Batman bathed in the waters. Batman was healed and slightly de-aged, while Sensei was killed since he was healthy.
Other Who have Used the Lazarus Pit
Kobra discovered the chemical composition of the Pit and was able to recreate them in order to bring his followers back from the dead. Jason Burr was also brought back from the dead in order to usurp his brother as the next Kobra.
Black Canary used the Lazarus pit to regenerate her Canary Cry and her ability to bear children.
Ra's had two daughters, Nyssa and Talia, who have also used the pits. Nyssa had used the pits to keep her youthful up until her death. Talia was placed in the pit after Nyssa killed her over and over again, healing her each time, in order to warp her mind into helping her.
King Snake uses the pit to regenerate his eyesight.
Batman put Bane in a pit in return for taking a bullet meant for Batman.
Mr. Freeze used a pit on his long comatose wife in hopes to revive her, however she absorbed its attributes, gaining the ability to control fire and reanimate the dead.
Cassandra Cain was also placed into the pit after being killed by Mad Dog of the League of Assassins. She then mortally wounded Lady Shiva in a duel and placed her in the pit as well.
After being resurrected, a mentally damaged Jason Todd came to live with Talia al Ghul. She decided to heal his wounds and throw him into the pit in order to discover the reason he had been brought back to life.
The Riddler, suffering from a brain tumor, secretly submerged himself in a Lazarus Pit in order to heal himself.
Dick Grayson puts what he believes to be Batman's corpse into a Lazarus Pit, only to discover that the resurrected body is that of a Batman clone created by Darkseid.
Dick Grayson also places Batwoman into the Lazarus Pit after she is mortally injured by an explosion.
In the Alternate Timeline story, Superman & Batman: Generations, Ra's al Ghul discovers a way to eliminate the madness side effects and develop a way to create lasting immortality. He offers Batman a chance to join him, but when they both submerge themselves in the pit, Ra's dies and Batman becomes partially immortal, aging one year for every century that passes.
Two Lazarus Pits appear in the Batman: The Animated Series two part episode "The Demon's Quest". One in Ra's al Ghul's mountain lair and another in his desert lair, where he seemingly falls to his death after falling into it.
A pit is shown briefly in the Superman: The Animated Series episode "The Demon Reborn"
Another appears in the Batman Beyond episode "Out of the Past" where Ra's al Ghul occupies his daughter's body and attempts to trick Bruce Wayne into possessing his body. At this point the rejuvenation process is much safer, however given Bruce's age, he would have had to bathe in the chemicals for a long time to make his rejuvenation permanent.
Jason Todd is brought back from the dead in Batman: Under the Red Hood by the use of a Lazarus Pit.