Skeleton Key

"If the stories are to be believed, this key will open nearly any ancient door".

Skeleton Keys are items used to unlock the roguelike sections of various challenge dungeons.

Obtaining
From quests:
 * One Skeleton Key, along with the blueprint, is given by Kalderos upon completing the quest Descent into Torment.
 * One Skeleton Key is given by Mogdrogen upon starting the quest Cleanse the Corruption.

From crafting:
 * A blacksmith can craft a Skeleton Key if the blueprint and the resources are available.
 * An inventor can produce a Skeleton Key when dismantling Epic or Legendary items.

Usage
Skeleton Keys are used to open the sealed entrances to challenge dungeons. The key is consumed upon use.

Challenge dungeons that require a Skeleton Key to open are:
 * levels 4 and 5 of the Steps of Torment.
 * levels 2-4 of the Bastion of Chaos.
 * Port Valbury.
 * The Feral Thicket in the Ancient Grove.
 * The Tomb of the Heretic in the Lost Oasis.