Many mnemothecae exist in the Dreamy Side. Most functioning ones are at the Necrode Capital.
These structures were created by the Artisans millennia ago to preserve information. They have been taken over, however, by the Necrode Kingdom, which uses them to store stolen memories and souls.
They typically consist of many corridors with piled shelves where vessels containing information are stacked. Taxergon type Onirodes keep such places organized.