Rooms that are part of the famous Opticording Sphere Quest have received the player-given name of forges because of the Opticorder Forge that is located in the first one. So far, four of such rooms have been discovered:

Oramond Forge

The Oramond forge. In it, you'll find a Broken Opticorder Forge

All of them can only be accessed after a unique riddle has been solved. They look very similar to one another and share many items, such as Stands, Crates, Buckets, Burnt Scrolls, and more. They also contain documents that tell more of the story behind the quest.

See also: Opticording Sphere Quest