The Russian paused for a moment and gave a very faint smile, but a smile as far as Russians were concerned.
"Let me put it in more easily understandable terms, Imagine briefing map, two directions maybe three if it is a model of a city for instance Berlin."
Gestures of his hands over the work table gave a bit of emphasis to the words that flowed from his mouth.
"Now imagine rather than just flat piece of paper it is something three dimensional that can rotate within table to show a new map of same place but it could be map from 1800, or 2000, It could even be map of different Berlin where War didn't happen in first place... Let us use six sided cube for simplicity for this object."
The Slav then pointed to his portal which sat unassuming like a gargoyle, yet as before had shown it could spring to life on demand.
"Now Imagine that gate as a switch, that when set correctly can Rotate cube and show new map at will."
his stony expression gave way to a slightly pleading one, as if to implicitly voice that the man was to take these secrets to his grave.
"I live here because it is actually safer here than Soviet Union. Where government would use power of this device to place 4000 Kilo bomb under enemy parliament building or heavily populated civilian sector without warning and detonate it with impunity. That is what this could do in wrong hands... and why it must never fall into hands of any military power. Soviet, German. Japanese, British, American, French... All of which could use device to take over world in matter of months...
His poker-face returned quickly after he caught his breath for a few moments.
"So... Is why I stay here... As such device is safe here too under watchful eyes of my colleges and myself... Keeping Pandora's box out of hands who wish to fully open it more than I already have comrade."
Rather than going into detail on what he meant on 'more than he already had' He began to delve into why he lived in this lonely and godforsaken world with only himself and his colleagues left.
"Here I can pursue other feats of engineering that are much less dangerous, things that even in my time were only seen in science fiction novels. But still this device is by-far the most powerful I have created... It is literally gateway to not just our universe, but many others as well."
His eyes narrowed ever so slightly to refocus on the German solider before him, and promptly reminded the man of his choice he had to make.
"It is because of this power you must make decision... I can send you back to whence you came if you desire... or I can work with you to find new place in multiverse to live the rest of your life in. It is very unlikely we will cross paths again at that point."