Zul'Farrak is a walled troll city nestled along the northern mountains of Tanaris. It is an outdoor instance, which means that players are allowed to use mounts in it. The adversaries here are hostile sand trolls, who have taken an expedition of explorers hostage at the massive pyramid in the city's center.
There are only two bosses that are mandatory to 'complete' the instance and get the achievement, but there are a number of optional bosses that most groups choose to down for gear upgrades. One of them is a witch doctor, who animates the corpses of the graves that surround him to aid him in his fight against you...
...and another summons waves of his pet basilisks to defend him.
When you reach the massive pyramid, you confront the jailer at the top, and free the imprisoned expedition members. Doing so triggers an event where one hundred trolls gather at the pyramid's base and storm up the stairs to fight you. Once you fight your way through, their leaders show up and you can finish them off. Once you do, one of the expedition members blows up the door leading to the instance's final boss. An old quest used to have you ask another expedition member to return something he had borrowed from someone in Gadgetzan. Doing so made him so angry that he and the rest of the expedition would attack you, meaning that you HAD TO SLAUGHTER THE PEOPLE YOU HAD JUST RESCUED.
Behind the blown-out gates you find the instance's unofficial boss, Chief Sandscalp, who fights you with his right-hand man
...but further into the zone is a mysterious pool with a gong next to it. Ringing the gong summons a giant lizard, Gahz'Rilla, who you can kill for additional loot.