Main Directories ?

How do you see a listing of the main directories, say from root or any other user.
I cannot remember the command to do it, but I know It can be done, cause I did it before. Let me explain fully.
I want to see on the command line the listings of all the main directories ie; /dev. /var, usr, /boot, /home, /etc.
Now when I use the ls -al command it only shows what is in that users directory.
So I hope I have made myself clear.
Thanks, Pat