Steven's Quarry is located just outside of Mystic Falls. The quarry has been a site for many events in timeline of the series; it was the place where Stefan and Damon woke up while in transition after being killed by their father, where Stefan thought of committing suicide, where the sacrifice to break Klaus' hybrid curse took place, and where Silas dumped Stefan and the safe, after Stefan tried and failed to bury Silas' once-desiccated body. At the bottom of the quarry, Stefan spent three months drowning, dying, and reawakening over and over again while trapped in the safe.
In 1864, both Stefan and Damon came back to life in transition to becoming a vampire. Emily and her brother had brought them there to recover. It was there that she explained to them that they were in transition, and that if they did not feed on human blood, they would die.
In Blood Brothers, after Elena accidentally let Stefan escape from the Salvatore basement, Stefan fled to the Quarry to order to commit suicide by waiting for the sun to rise without his daylight ring. Elena eventually found him and talked him out of killing himself, with Damon's help.
In The Sun Also Rises, Klaus chose this spot as the location where he would break his hybrid curse by sacrificing a werewolf, a vampire, and a Petrova doppelgänger. At this location, Jenna, Jules, Greta and Elena were all killed, but Elena was able to be resurrected by a spell performed by Bonnie Bennett, using John Gilbert's life force. Klaus was nearly killed by Bonnie and Elijah at this site, but Elijah eventually changed his mind and saved his life, instead.
In Graduation, Stefan planned on dumping Silas' petrified body into the quarry, but it was revealed that Silas was no longer neutralized, as the spell that Bonnie used to desiccate him was tied to her life, and when she died, the spell broke. Silas then incapacitated and locked Stefan into the safe, and proceeded to dump it into the quarry.
In True Lies, Stefan was still suffering while Damon has Sherrif Forbes and her men search the waters for Stefan. Later his safe was found a few miles away from the quarry, in the woods. When the safe was opened by Sheriff Forbes, Stefan was nowhere to be found. Instead, there was a dead corpse with its throat cut out.
In Original Sin, it was revealed that the safe Stefan was locked in all summer was fished out by the man in the safe, on the newly-resurrected Qetsiyah's orders. She continued to stay at the now-dead man's cabin near the quarry as she plotted Silas' death.
In I'm Thinking Of You All The While, Stefan and Elena said goodbye.