ISO image files (*.iso) are useful things. They were originally developed as a standard for storing data on CD-ROM, and hold not just files but also all their associated data structures as well -- things like directories, file attributes and boot code - which geeks call 'metadata'.
ISO files are often used for backups, though people are more familiar with them as being an intermediary stage when duplicating DVDs. And most people think that to get at their contents you need to 'upack' them somewhere -- onto a hard drive or optical disc. But under Linux you can simply mount them on your operating system.
Suppose I have an ISO image called bachups.iso from which I want to extract a single file. To look at it, I first need to create a mount point on my system: