No additional software required. First, create a directory in which to mount the ISO.

mkdir -p ~/media/iso

Then, to mount it:

sudo mount -o loop /home/path/to/my_fun_dvd.iso ~/media/iso
nautilus ~/media/iso

The last line is to open the mounted directory in a visual file browser called Nautilus.

If you end up doing this often, you can create a bash function. Put this at the end of your ~/.bashrc file:

function mountcd {
sudo mount -o loop $1 ~/media/iso
}

Save the file, reload it in bash using this command

. ~/.bashrc

That’s (period)(space)~/.bashrc — the period is a command in bash that reloads the script file without having to launch the terminal again.

Now you can do this in the terminal:

mountcd ~/Downloads/my_cool_dvd.iso

And your DVD ISO will be ready for viewing in the ~/media/iso directory (the tilde character means your home directory, /home/john). In Ubuntu 12, by opening the folder containing the DVD files, it will prompt you to open with VLC media player: