The Dream Machine is never seen in Keen Dreams but it brings Keen to the land of Tuberia, and he must deactivate it in order to free all the enslaved children. (None of which are seen during Keen's travels.) We are informed however that it has a number of complex readouts and dials as well as a large red level labeled "On/Off switch" which controls the machine.
The Dream Machine is obviously built with technology far surpassing the primitive means of the tuberians who seem to still be stuck in the iron age. It is not known who or what built the Dream Machine, nor how they did so and bought it to Tuberia. Mortimer McMire is implicated...
Keen does not destroy the Dream Machine, he only deactivates it, leaving open the possibility that it may simply be reactivated and used again. Since this has not happened it can be assumed that only King Boobus Tuber had been informed on how to use the machine, or alternatively that anyone who can operate the machine has not visited Tuberia recently.