To switch from the GUI desktop in Linux, you can use CTRL+ALT+F1 to switch to
tty1. Use F1 through F6 to access tty1 through tty6.
Once you are in a tty virtual console, you can just use ALT+Fn to switch
between the six consoles. The logged in GUI desktop is on tty7(1) so you can
get back to X-Windows with ALT+F7.
(1) - At least on my Raspberry Pi. I have read that newer versions of Ubuntu
use tty1 and tty2 for the login screen and user desktop respectively.