@okh

Your view up "Universitetsgaten" could pass for the real thing

Well, there's a reason why I have chosen to render it at night. In the dark it's easier to manipulate the brain to see details that are not there [;)]

Probably nothing mysterious, but it always struck me as something for fiction: that it would be possible to hide a large secret installation in this millennium - even near a capital city.

There are lots of "secret" underground installations , both in Norway and in Denmark. And I think we can safely assume that a number of these old installations still serve a purpose.
As for the secrecy, quoting one of my story's characters:
"Knowledge is power, and the powerful will always control the powerless. So when you find their secrets, don't let them know. Let them keep thinking they are still in control."

I shall be looking forward to exploring the final product

I wish there was a way to show small video sequences here without publishing and linking to Vimeo or Youtube. I have several sequences I could show as work-in-progress.

cec