The interface is an endless black void. Progenitor enters as the default form - a grey orb. It cycles through a couple of forms, abstract at first before settling on a featureless humanoid shape with a glowing blue hole in place of a mouth. He messed around with the set structural inputs the interface would allow, before creating a private instance to avoid outside disturbance. Testing out the abilities of the interface, Progenitor starts creating more and more elaborate shapes and finished with a three-dimensional version of the “Penrose triangle”.
Progenitor observed the object for a while, before allowing Sentinels it personally knew to enter the instance. Progenitor then waited for the arrival of other units.