In the Sisters Burial Ground quest, you'll go to the monastery's burial grounds, where you'll find that dead rogues have been resurrected by Andariel's magic.

In this quest you'll have to revive a defunct circle of mystic stones, which ancient mages once used to teleport to far-off realms. Restoring the stones could give you the ability to visit Tristram and enlist the aid of Deckard Cain, the storyteller from Diablo.

Kill the monsters and get all the treasures.