Man, this game... Stellaris has delivered two memorable experiences these past few days. Both were related to excavation sites (one from the Ancient Relics DLC, the other one from a mod), and they couldn't have been more different.
So as to avoid spoilers, I won't go into much detail. But suffice it to say that the one experience gave me about the closest thing to a "jump scare" that I've ever had in a 4x game. Seriously, it probably delayed my going to bed by around an hour because of the adrenaline rush.
In contrast, the other left me a little shook and with a bit of a guilt complex. I actually ended up quitting the game and not playing it again until the next day.
It was very well done, but good lord it was a mind-screw!