The Offline Files (Client Side Cache, or CSC) folder/database comprises multiple folders and is located in the %SystemRoot%\CSC folder by default. The CSC folder is hidden by default and should not be modified in any way. Doing so can cause cache corruption or can cause Offline Files not to work at all. Should this occur, see the following article in the Microsoft Knowledge Base:
How to Restart the Offline Files Cache/Database
The Offline Files folder structure has the following layout:
CSC (parent folder)
Folders D1-D8 are the holding areas for cached data. The cached files are placed into these folders in binary form. Within the parent folder (CSC), additional files are created to hold operational data needed for the operation of Offline Files.
The cache viewer reads the data from the folder structure and displays it in a readable format.
The database folder layout is verified upon Windows startup or the reactivation of Offline Files and checked for consistency. If a folder is missing, it is re-created automatically. However, a cache reset is performed automatically when this occurs, clearing the previous contents of the cache.