The elevator in Tarkus that is supposed to lead down to planeside has no options to descend. Basically stuck in the area with the dockmaster and no way to continue
You don't take the elevator down, you take the stairs on the right. Eventually, you will find out where the elevator goes (it's a quest), and then the comment in the elevator will be along the lines of "pity they can't fix this, it would save you some walking."
This trips players up from time to time, but the button to use the stairs is on the sidebar on the left. Step onto the stairs tile on the map, and you should be able to use the stairs button.