The Spider Forest is the first jungle ara in Act 3. It includes the entrances to two dungeons - the Spider Cavern and the Arachnid Lair. The waypoint always appears near one of the two dungeons.
When the player leaves the Kurast Docks for the first time, they will encounter the Dark Wanderer himself. After a short while, the Wanderer disappears in a flash, spawning several Flesh Beasts after vanishing.
The Spider Forest is connected to not one, but two other wilderness areas: the Great Marsh and the Flayer Jungle.