When you create Layers inside Sandbox, a "Layers" sub-folder is created in your level folder. Each layer gets its own .lyr file which allows for collaborative editing. If a layer inside Sandbox has sub-layers within it, another sub-folder is created.
Backup files are automatically generated by Sandbox each time you save your level. When you save over your .cry file, your existing .cry file is renamed to .bak and if in the event a .bak file already exists, .bak2 is created as a secondary backup. These .bak files are exactly the same as the .cry file, only with renamed extensions.
If you wish to use or restore from a backup file, there's two ways in which you can do this (using Forest as an example):
- Rename the Forest.bak file to Forest.cry. When prompted about changing the extension, select 'Yes'.
- Open the Forest.bak file in Sandbox (you'll need to view "All Files") then "Save As" the Forest.cry file.