Accessing the HEMMER cluster and GRID from outside NTNU is normally restricted. Also might be restricted when using WiFi.
One way to connect to them is either to connect to VPN or to use the login.(ansatt | phys | stud).ntnu.no as jumphosts. This usually means slow sessions or unresponsive X11 GUI sessions.
One way to make it faster is to use SSH tunnels, and better SSH multiplexing.
To make it easier, here is a script that creates a function to do all that with a single command.