If you are looking for a comprehensive guide or a "megathread" style post regarding decrypted 3DS ROMs on Archive.org

files. If they are truly decrypted, the game icons will appear instantly. Storage Space:

The Best Legal Workflow: Buy a used 3DS game on eBay. Dump it using a modded 3DS and GodMode9 to create a decrypted .cci file. You now have a permanent, legal, decrypted backup.

Warning: Unlike officially archived books or music, these 3DS files exist in a legal murk. The Internet Archive removes these files when they receive DMCA takedown notices, but due to the sheer volume of uploads, many remain accessible.

He opened the text file. It was a readme, a digital message in a bottle.

.CIA (CTR-Image-Archive): These are "installable" files. On a modded 3DS, you use a homebrew app called FBI to install these directly to the Home Menu.