The architecture of Europe tends to be mind-blowingly big, incredibly old, and spectacularly beautiful. Perhaps the greatest example of this, architecturally, is the massive Notre Dame Cathedral.
Having interesting stuff to look at is one of the make-or-break features of stealth games. Like when I'm hiding in the bathroom at work during performance review week, it really helps if there's a good magazine or some interesting limericks.
Because of this, when the famous medieval-stealth-game-meets-ridiculous-alien-conspiracy series, Assassin's Creed, chose the French Revolution for the setting of their eighth title, architecture became doubly important. For Notre Dame Cathedral, the crown jewel of pre-industrial architecture, it was imperative that they get everything looking good enough to make gamers gasp. Do things right, and the game would have a spectacular-looking landmark for promotional material, and for gamers to climb all over (an act that is discouraged by France's no-fun IRL tourism board).
So, Ubisoft appointed someone to work on this task full time. As in, their entire job would be painstakingly recreating the cathedral, brick by brick, until they finished a masterpiece or went insane, or maybe both.
The developer was Caroline Miousse. Working with an architect, she painstakingly began the process of recreating the cathedral brick by brick, and continued this work for TWO WHOLE YEARS.
That, in and of itself is a crazy-daunting task, but there were several obstacles that made designing the church even more difficult. First of all, a lot of the dazzling art in Notre-Dame Cathedral is protected by copyright law, so Miousse had to design her own art and rival the works that took groups of artists hundreds of years to create. Also, the game wasn't set in the present, it was set during the French Revolution, leaving Miousse the unenviable task of researching exactly what the place looked like hundreds of years ago.
Another difficulty is that Miousse hadn't actually visited the real cathedral. She pressed on, however, and succeeded nobly, creating one of the most spectacular buildings in the video game universe.