The Abandoned Farm is a relatively small area in Diablo III that's only accessed from solving the Map of the Stars riddle, and only during The Darkening of Tristram event.

Poking the dead cows near Adria's Hut in the order of Middle Cow, Left Cow, Right Cow will cause the ground near a dead tree to light up, but only if you have the Map of the Stars item. If not, then you will have to try again when you have said item. The area is populated with a large number of cows that are not threatening to murder you. Near the center of the area is a chest supposedly belonging to Wirt, containing his stash and the pet Royal Calf.