The Abandoned Cellar is a location in the Stinging Winds in Act II of Diablo III. The entrance does not appear on the mini-map until the player clicks to open the cellar doors.
In the cellar one can find Dark Cultists and a Superunique Grotesque called Ekthul. A prisoner NPC will thank the player within the cellar and grant them access to a chest.
Entering the cellar adds to the Nooks and Crannies achievement.