So what I do is,
sudo mount -r -t iso9660 [path-to-iso-file] -o loop /media/cdrom0
If you are on other linux, you probably need to ditch the sudo, and do it as root. Probably modify /media/cdrom0 part too
So example on red alert ISO I downloaded. and unzipped at home directory, the command would be:
The command above is actually in one line.
sudo mount -r -t iso9660 redAlert/RedAlert1_AlliedDisc/RedAlert1_AlliedDisc/CD1_ALLIED_DISC.ISO -o loop /media/cdrom0