The Caverns of Araneae are a location in Act I of Diablo III. Previously an important passage to the highlands north of Wortham, nowadays only the most hardened adventurers are able to pass through these passages, after it became infested by spiders and their queen, Queen Araneae. Various egg sacks and cocooned victims contain gold and treasure.
The Dusty Leather satchel, containing Torn Letter's Response, is found here as well.
Upon killing the queen, NPC Karyna, who is trapped in a nearby web, will ask to be freed, using acid from a nearby pool. She will want to get out of this place as soon as possible, before she goes mad. The way into the Highlands Crossing will become open, through the vacated web barrier.